Nextcloud
Nextcloud is a self-hosted file-sync application written in PHP. We've used it pretty heavily for many years now (and ownCloud, its predecessor, before that). Despite being a pretty nifty package in a lot of ways (especially as a concept), it increasingly has lots of little problems that are making it more and more difficult to use and maintain.
The following issues are in no particular order.
Issues
Web UI
Upgrade Button Unresponsive
When there is an upgrade available, the "Open updater" button on this page --
-- will often be unresponsive for a long time, even after all the security checks (above it on the page) have finished. Usually if I go off and do something else for about 10 minutes, it will become live and I can then start the upgrade. This has been a problem through at least a few major versions now.
Mobile UI
Uploads Get Stuck
Sometimes automatic uploads just stop, for no apparent reason, and give very little information about why. Why is it "Waiting to upload"? What is it waiting for? Tapping or press/holding an individual file might get more information, or might not. Sometimes it will get the process started, but often nothing happens and you can't tell if it's locked up or overloaded or if it's not supposed to do anything when you do that.