Task duration incrrectly dispalyed in Gant

Hi

I have a server with three sites(multitenant) . 3 months ago I upgraded from V13 to V14. I have in the meantime discovered that Gant view on my one site does not work properly. While it was still on V13 it worked fine. NOw, on the one site, the task-duration on Gant view is 3 days, irrespective of the actual task start and end dates. I checked it on the second site and it seems to be fine there.

I have just done an update --reset to the latest V14, hoping that it will solve the problem but it still does that.

I checked the database and the dates are atually correct in the database.
Calendar view seems to be fine.

Someone perhaps have a suggestion where I can start looking ?

Isnt there anyone that perhaps has a suggestion on this one, please ?