zephyr: Upload halts, keeps spinning in cbor decoding (nrf5340)

[peran1337]

I have an issue I have traced to the file cborattr/src/cborattr.c. I updated my nrf5340-based application from NCS 1.5.1 to 1.6.1 and then my FOTA upgrades stopped working. I can upload the netcpu update without issue. With the appcpu a good chunk of the file is uploaded, but then the system starts spinning. For each iteration it is executing cbor_value_advance() (line 309). Before that call I examine the struct CborValue cur_value and I find that the value remaining never decreases, the type is CborSimpleType, offset increases by 1 per iteration, and length (found using call extract_number) grows by one per iteration. (Quite different from how it is during normal operation.)
I tried reverting my branch to before the move to 1.6.1 and build that. It also failed while uploading (to a 1.6.1 system).
Attached are debug output from mcumgr, runtime output from appcpu, and a diff showing the modifications I made to obtaim this log.
diff.txt
mcumgr_debug_log.txt
runtime_log.txt

[peran1337]

mcumgr_debug_log is not from the complete transfer. However, it does include both before and after the critical section. When piping the output to file, I lost formatting for some reason (everything was enclosed in " " so newlines were no longer recognized), making it totally unreadable. We had a short meeting in the local LUUG discussing it :D So this is just copy/paste from terminal window.