The Syncthing build seems to crash when run on a Raspberry Pi 4, and another device tries to synchronize lots of data from the Pi.
The crash log begins with:
$this->bbcode_second_pass_code('', '
runtime/cgo: pthread_create failed: Resource temporarily unavailable
SIGABRT: abort
PC=0x76dfe104 m=2 sigcode=4294967290
goroutine 0 [idle]:
runtime: unknown pc 0x76dfe104
stack: frame={sp:0x66b4d968, fp:0x0} stack=[0x6634e214,0x66b4de14)
')
This doesn't happen with the official arm build (through the syncthing-bin aur package).
GitHub Issue (which contains the full crash log) and forum post with some more discussion.
Thanks!