Hello,
- tools probably do not have impact on this and there were no update for MbedStudio in last few weeks
- an error in your code is very likely, but you said you changed nothing
- an error in MbedOS is also very likely, but you said you changed nothing
With this description it is really hard to say what can be the reason. You can try to debug your code, if is that feature available for your target or debug via the printf to dedicate where exactly the program crash.
If you not do not use a repository for your project and its Commits until now, maybe you have good reason for that now.
Did you try to create a new empty program and copy only the content of your code?
And also version of Mbed OS that you use could be good information.
There were strange issue with Mutex and a MAXim target last year (not verified) - Using std::printf causes a mutex error? - Mbed OS / Hello world! - Arm Mbed OS support forum
BR, Jan