This likely indicates a memory corruption. This error means that the most significant bit of the s_FastSemihostingState.WriteOffset variable (0x80000000) is set, which is a special value reserved for the resource manager API. If you are not using the resource manager, something likely overwrites WriteOffset with an invalid value.
Memory corruption problems could be tough to pinpoint. The easiest way to handle it would be to revert to the last version that worked via your source control (or re-create the project from scratch, if it is trivial). You can also try setting a breakpoint in WriteRawFastSemihostingData() and observing how it changes s_FastSemihostingState.WriteOffset (it’s a simple ring buffer that is written by the firmware and read by VisualGDB), although it could take some time to find the root cause this way.
I made a new clean project with only one printf() function in loop along with 1 ms delay between and found I still getting this overflow state. No error masseges however. I was ready to report it to you but after new reflash problem suddenly dissapeared.
Now I wrote my last firmware with a problem again and now it works without any issues also. I really don’t know what was that. I worked much more then 8 hours today and maybe I made some stupid mistakes but also maybe it somehow related to things I have done.
Anyway. Thank you for your time. I’ll report you in case I’ll get clue or additional useful info.