Very interesting you’re able to reproduce this on try, because I’m not:
(In Firefox 97 on Linux)
(The date is still wrong since it is showing up on the 10th, not on the 11th, but it’s not showing up in march…)
Even in Browserstack on Windows 10 and Firefox 99 it seems to work fine (except for the background color of the task):
I think you’re hitting a variant of this: Gantt display wrong
What locale and time zone is your browser set to?