Installing on external SSD

Since Day 1 of using MSFS i have a very strange problem. This does only occure with MSFS, so i am quite sure that this must not be a hardware but a Microsoft Store issue:

I install MSFS, then load all the sceneries and aircraft within MSFS. Then it works perfectly. But as soon as there is an update for MSFS i am not able to download the Program itself anymore. I get the info that there is a new version and i have to download it in the Microsoft Store. There i can start the download but from the program loads endlessly (i see activity LED flickering on the external SSD as well) but the download of the program never ends. In that case i have to uninstall, wait a few days, download the SIM again and hope that there is no update soon.

So in i nutshell the problem is: I can download MSFS and everything in one step - but as soon as there is an update the update process does no work.

Could this be an issue with the Microsoft Store? Any advice?

best regards
Michael