1. Close all debug windows in winIDEA.
2. Run the application from the reset state on. This ensures that the debugger doesn’t access any Target CPU resources while the application is running. This also best mimics Target running standalone without the debugger connected.
If this solves the problems, it means that earlier, one or more debug windows with specific configuration (real-time update enabled) were opened and affecting the run-time application execution time.
3. Open debug windows of interest one by one and each time run the application from the reset state on to confirm it's still running properly respectively unaffectedly by the new debug window.
Several debug windows can be configured for real-time update. Most often is the Watches window. If real-time update is enabled, there should be no problems as long as only a few variables are observed in the window. However, if a (larger) structure is observed, this could affect application execution time. Either remove such a structure from the debug window or simply disable Real-time update for the whole debug window during the troubleshooting of this problem.
The real-time update is available also for the Memory window and Special Function Registers window but these two have it disabled by default since it's highly likely they generate such an amount of memory accesses toward the target CPU, that the application execution time gets affected. It's never recommended to use real-time update for these two windows unless you have a specific debugging use case and you are fully aware of possible consequences on the application execution time.