Uploading Arduino M0 takes a long time with the Arduino Web editor

I have been using the Arduino Web Editor when I am teaching children. It works great with the Arduino UNO, I have the impression it compiles and upload even faster than the Arduino IDE. On the other hand, with the M0 I get the following messages while uploading, and it takes a couple minutes to complete:
Restarting in bootloader mode

Get port list before reset

[COM4]

Touching port COM4 at 1200bps

Set DTR off

Flashing with command:C:/Users/.arduino-create/arduino/avrdude/6.3.0-arduino9/bin/avrdude.exe -CC:/Users/.arduino-create/arduino/avrdude/6.3.0-arduino9/etc/avrdude.conf -patmega2560 -cstk500v2 -PCOM20 -b57600 -Uflash:w:C:/Users/AppData/Local/Temp/arduino-create-agent209593565/DemoReel100.hex:i

avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.00s

avrdude: Device signature = 0x1e9801 (probably m2560)

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: NOTE: "flash" memory has been specified, an erase cycle will be performed

To disable this feature, specify the -D option.

avrdude: erasing chip

avrdude: reading input file "C:/Users/AppData/Local/Temp/arduino-create-agent209593565/DemoReel100.hex"

avrdude: writing flash (42980 bytes):

Writing | ################################################## | 100% 0.28s

avrdude: 42980 bytes of flash written

avrdude: verifying flash memory against C:/Users/AppData/Local/Temp/arduino-create-agent209593565/DemoReel100.hex:

avrdude: load data flash data from input file C:/Users/AppData/Local/Temp/arduino-create-agent209593565/DemoReel100.hex:

avrdude: input file C:/Users/AppData/Local/Temp/arduino-create-agent209593565/DemoReel100.hex contains 42980 bytes

avrdude: reading on-chip flash data:

Reading | ################################################## | 100% 0.27s

avrdude: verifying ...

avrdude: 42980 bytes of flash verified

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: stk500v2_ReceiveMessage(): timeout

avrdude: safemode: Fuses OK (E:50, H:58, L:50)

avrdude done. Thank you.

Any suggestions what could be wrong?

Here another report

I cannot see any error in this output. The system just reinstalled the bootloader but seems like it worked and successfully wrote on the flash. What is the exact issue you encounter?