Success! I've been reading and measuring and soldering everything to fix the bug. With some datasheet help and my trusty multimeter. I did the following fix: Soldering the SCK pin (only soldering this pin does not fix the CRC errors) Soldering pin 7 to pin 8 on the flash chip finishes the fix. So first my log shows: OTA:FWP:FL DUMP 437A:0000000000000000000000000000000018530 Now the log shows TSF:MSG:READ,0-0-45,s=255,c=4,t=3,pt=6,l=22,sg=0:03000D0003000C94D5030C94D5030C94D5030C94D503 OTA:FWP:FL DUMP 003A:0C94D5030C94D5030C94D5030C94D503127516 Lot more data is whriting to the flash. And after the firmware is recieved: 127760 OTA:FWP:FW END 129652 OTA:CRC:B=04E0,C=3E27,F=3E27 129656 OTA:FWP:CRC OK And the node reboots so OTA works! And as a bonus #define MY_OTA_FLASH_JDECID (0x1F65) Works also so this can also be used as an red flag if your OTA is not working and you have the correct flash chip but get a FLASH INIT error. I would like to thank everybody for helping! @sundberg84 I would not move away from your great PCB design, but I might order some new ones.

@jkandasa Brilliant - thank you!!!

I don't know why but now OTA works better; I still get quite some NACKs on the gateway but at least most of the times the OTA is successful even with signing enabled. With ACK enabled the transfer speed is at least 4/5 times slower

@jkandasa Great! Thanks for pointing me out. I'll take a look. Regards