Nodemcu troubleshooting

We are going to use Serial.communication between Arduino and NodeMCU. Now we have a problem with the NodeMCU sending error codes. It worked perfectly for some time ago while using Nodemcu for another project, now Serial.print does not even work, it keeps reseting and sending these error codes.
I have also tried with batteries to check if there was because of not enough current.

.
WiFi connected
Server started
192.168.10.200

 ets Jan  8 2013,rst cause:4, boot mode:(3,6)

wdt reset
load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v4ceabea9
~ld
0.0.0.0


Connecting to krille25

Exception (9):
epc1=0x4021a0f5 epc2=0x00000000 e
Exception (28):
ep
Exception (28):
ep
 ets Jan  8 2013,rst cause:4, boot mode:(3,6)

wdt reset
load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v4ceabea9
~ld
0.0.0.0


Connecting to krille25

Exception (0):
epc1=0x4022b063 epc2=0x00000000 epc3=0x00000000 excvaddr=0x00000000 depc=0x00000000

ctx: sys 
sp: 3ffffc30 end: 3fffffb0 offset: 01a0

>>>stack>>>
3ffffdd0:  3fff0b70 3fff0ba5 3ffe9886 3ffe9880  
3ffffde0:  00000001 3ffed3c8 3fff0d4c 3fff18dc  
3ffffdf0:  00000011 00000001 3fff0b70 3fff188c  
3ffffe00:  3fff0b74 4020a39a 3fff0b70 40210516  
3ffffe10:  00000000 00000000 00000000 00000016  
3ffffe20:  40101be1 3ffed6c0 3fff0b70 4020a439  
3ffffe30:  00007fff 3fff183c 3fff0b70 4020d988  
3ffffe40:  c80aa8c0 00000000 00000000 4010020c  
3ffffe50:  010aa8c0 00ffffff 3fff0b70 4020d9db  
3ffffe60:  3fff1814 3fff0b70 3fff1814 4020f3b8  
3ffffe70:  010aa8c0 00ffffff 3fff1814 3fff188c  
3ffffe80:  3fff1814 3fff0b70 3fff0c4c 4020fbb5  
3ffffe90:  c0a80a01 40101f8c 3fffc200 00000022  
3ffffea0:  00000000 00000123 3fff18c6 3fff0c28  
3ffffeb0:  0000011f 3fff0c4c 000000f0 00000004  
3ffffec0:  00000004 00000004 00000000 3fff188c  
3ffffed0:  0000012c 3fff17e0 0000000a 3fff188c  
3ffffee0:  3fff0c58 3fff18be 3fff185c 3fff188c  
3ffffef0:  3fff0c58 3fff18be 3fff185c 4020dc48  
3fffff00:  00000000 00000043 3fff0b70 00000000  
3fffff10:  00000000 00000156 3fffff80 3fff18aa  
3fffff20:  3fff0b70 3fff188c 3fff0c58 40211018  
3fffff30:  00000014 0000016e 0000016e 3fff0b70  
3fffff40:  3fffdc80 3fff110c 3fff17e4 3fff1184  
3fffff50:  00000008 3fff0b70 3fff188c 4020a779  
3fffff60:  3fffdc80 3fff110c 3fff17e4 401045cc  
3fffff70:  4022792a 3fff110c 3fff17e4 40227958  
3fffff80:  3fff189c 3fff188c 00000000 3fffdcb0  
3fffff90:  4022289f 00000000 3fff17e4 402299a7  
3fffffa0:  40000f49 3fffdab0 3fffdab0 40000f49  
<<<stack<<<

 ets Jan  8 2013,rst cause:4, boot mode:(3,6)

wdt reset
load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v4ceabea9
~ld
0.0.0.0

This message is repeating.

wdt reset
load 0x4010f000, len 1384, room 16 
tail 8
chksum 0x2d
csum 0x2d
v09f0c112
~ld

 ets Jan  8 2013,rst cause:4, boot mode:(3,6)

cause 4 is watchdog reset. something takes long time and the wachdog timeout runs out

We have tried flashing it and testing different codes which have been working before. We accidently connected the 5 volt arduino tx to NodeMCU rx (3,3 volt), may it be broken because of that?

krille105:
We have tried flashing it and testing different codes which have been working before. We accidently connected the 5 volt arduino tx to NodeMCU rx (3,3 volt), may it be broken because of that?

no, the esp8266 io pins are 5 V tolerant