Hi Bruno,
We recently upgraded TMS WEB CORE from 2.5.0.0 to 2.5.1.0 and saw below issue:
We debugged and finally narrowed down the issue to FNCProgressBar. After replacing FNCProgressBar with TWebProgressBar, everything is ok without issue on version 2.5.1.
On an another test, we downgraded the TMS WEB Core to 2.5.0, we did not see this issue anymore for FNCProgressBar.
Unluckily, we can't replicate this on a demo, and we hope what we identified so far can help you to debug this a bit easier.
Thanks,