Strange "Symbol not found error"

Using Connect IQ SDK 4.0.3 I get a strange error reported to the console:

Error: Symbol Not Found Error
Details: Failed invoking <symbol>
Stack:

No other details are provided, and the watchface app continues running apparently normally.

The error seems to occur when the background temporal event is run.

Running in Debug mode doesn't help narrow down where the problem is.

Also the error occurs when running some watch models like Fenix 5X, Chronos but not others like Vivoactive 4, 4S

I thought maybe the program is running out of memory when it receives data from a JSON request in the background temporal event,

but the simulator reports I have more than 11k of margin and I don't get an error -403 from the JSON request, which I have seen when

the memory limit is exceeded.

I tried to make a stripped down version of my app to send to you that exhibits the problem but so far haven't been successful at this.

Any hints ?