Unable to remove app from ios 12.2

Hi.

I’ve recently installed nextcloud app on my IPhone 7 (ios 12.2). I think I’ve done something wrong. I’ve tried to uninstall the app while it was sending photos to the server (problem with the cache no more space left of the phone). The app seemed to have been removed, but when I restarted the phone, the app was still here. However the nexcloud icon had changed. The icon is now a white square with a grid. When I tap this icon, a black screen appear and close immediatly. If I try to uninstall it again, the icon disappear but the app in the apple store is marked as already installed. If I restart the phone, the white nextcloud icon appear again …

I’m not sure if the problem is nextcloud app or the iPhone. If someone has ideas or clues for what is happening…

Thanks for your help