Problems with date formats making the app unable to read excel sheet

[Olemarthin1]

Hi,

I have made an app we use at work to track progress of our client work. The powerapp works mostly as intended, but have one major problem. The app has drop down boxes, and some date sections that users change and submit the update. Sometimes the dates in excel is made into a format that the app then later cant read. Users then get an error when trying to access the app, saying the app cannot read the content of the excel sheet. When I open the excel sheet, some of the cells with dates show as ############, and has to be replaced before the app can work again. I have a hard time finding the cause, as sometimes it happens several times a day and sometimes not for a few weeks, but its always the same problem when it happens. 

Has anyone experiences something like this before?  Would really appreciate any help one this issue.