Have the same issue as others on here. EMclient syncing with infomaniak. Enter a task in emclient with tomorrow as the due day and in infomaniak it goes in the day after tomorrow. Adding a reminder to stop the 00.00 issue makes no difference. If I add a task in Infomaniak for Friday, it comes back to EMclient as due on Thursday! With the greatest respect, I do not think this is a nextcloud issue as mentioned earlier as Infomaniak runs its own proprietary platform.
Just opened an account with fruux and exactly the same result.