I have a similar problem. For several days I was able to upload sketches to my Arduino Uno WiFi, but now I get the following:
FQBN: arduino:avr:unowifi
Using board 'unowifi' from platform in folder: C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6
Using core 'arduino' from platform in folder: C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6
Detecting libraries used...
C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO_WIFI_DEV_ED -DARDUINO_ARCH_AVR -DESP_CH_UART -DESP_CH_UART_BR=19200 -IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\cores\arduino -IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\variants\standard C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255\sketch\FirstProgram.ino.cpp -o nul
Generating function prototypes...
C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-g++ -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -flto -w -x c++ -E -CC -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO_WIFI_DEV_ED -DARDUINO_ARCH_AVR -DESP_CH_UART -DESP_CH_UART_BR=19200 -IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\cores\arduino -IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\variants\standard C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255\sketch\FirstProgram.ino.cpp -o C:\Users\Paul\AppData\Local\Temp\22913194\sketch_merged.cpp
C:\Users\Paul\AppData\Local\Arduino15\packages\builtin\tools\ctags\5.8-arduino11/ctags -u --language-force=c++ -f - --c++-kinds=svpf --fields=KSTtzns --line-directives C:\Users\Paul\AppData\Local\Temp\22913194\sketch_merged.cpp
Compiling sketch...
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-g++" -c -g -Os -w -std=gnu++11 -fpermissive -fno-exceptions -ffunction-sections -fdata-sections -fno-threadsafe-statics -Wno-error=narrowing -MMD -flto -mmcu=atmega328p -DF_CPU=16000000L -DARDUINO=10607 -DARDUINO_AVR_UNO_WIFI_DEV_ED -DARDUINO_ARCH_AVR -DESP_CH_UART -DESP_CH_UART_BR=19200 "-IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\cores\arduino" "-IC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.6\variants\standard" "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255\sketch\FirstProgram.ino.cpp" -o "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255\sketch\FirstProgram.ino.cpp.o"
Compiling libraries...
Compiling core...
Using precompiled core: C:\Users\Paul\AppData\Local\Temp\arduino\cores\arduino_avr_unowifi_878644b951ae49ec9ca42b57f4c6dd64\core.a
Linking everything together...
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-gcc" -w -Os -g -flto -fuse-linker-plugin -Wl,--gc-sections -mmcu=atmega328p -o "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.elf" "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255\sketch\FirstProgram.ino.cpp.o" "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/..\..\cores\arduino_avr_unowifi_878644b951ae49ec9ca42b57f4c6dd64\core.a" "-LC:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255" -lm
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy" -O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0 "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.elf" "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.eep"
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-objcopy" -O ihex -R .eeprom "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.elf" "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.hex"
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avr-gcc\7.3.0-atmel3.6.1-arduino7/bin/avr-size" -A "C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.elf"
Sketch uses 922 bytes (2%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
"C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino17/bin/avrdude" "-CC:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino17/etc/avrdude.conf" -v -V -patmega328p -carduino "-PCOM11" -b115200 -D "-Uflash:w:C:\Users\Paul\AppData\Local\Temp\arduino\sketches\27E7684CF380E7329EF8DFA057196255/FirstProgram.ino.hex:i"
avrdude: Version 6.3-20190619
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2014 Joerg Wunsch
System wide configuration file is "C:\Users\Paul\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino17/etc/avrdude.conf"
Using Port : COM11
Using Programmer : arduino
Overriding Baud Rate : 115200
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0xbe
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0xbe
avrdude done. Thank you.
Failed uploading: uploading error: exit status 1