As I reported HERE: Start tabs in a separate process, very often single tabs/tabs in a Dopus window crashed/froze on me (in WIN-Taskmanager: "No feedback"), while other opened Dopus windows were still open and working.
At least for me I found the CAUSE and therefore also the SOLUTION:
In my WIN task manager were very many processes "prevhost.exe" open, which is probably the preview of documents in the preview window don DOPUS. I work with it very much and if I close the respective preview window, the started process "prevhost.exe" does not seem to be terminated. When I open the preview window from another document, a new process "prevhost.exe" is apparently started, but when I close this preview window, this process "prevhost.exe" is not terminated either ... etc. etc. ... with the time therefore more than 10 to 15 running processes "prevhost.exe" came up with me (visible in WIN-Taskmanager).
MY (simple) SOLUTION now: When I had terminated more than half of these processes "prevhost.exe" in my WIN-Taskmanager, suddenly the just crashed/frozen Dopus Register/Tab was clickable again and I could continue working.
Which document types and viewer were being viewed that caused those prevhost.exe processes to launch?
Does the same thing happen in File Explorer?
It can be normal for prevhost.exe to stay running for 10 minutes or so, although when it does it should usually be recycled if you view another document of the same type.
Basically I preview only PDF documents with (the plugin from) trackersoftware (PDF editor, currently version 7.0, build 328.1, Dec 16 2018).
I don't use WIN Explorer (file manager) anymore since I use DOPUS, so unfortunately I can't say anything about the behavior in this WIN file manager.
If the same issue also happens there, then we know it isn't specific to Opus and it's best reported to Tracker so they can look into it.
But if it only happens in Opus, it might be something we're doing wrong on our side.
When things are stuck, taking a few process snapshots of prevhost.exe, as well as dopus.exe and any docsvw32.exe / docsvw64.exe processes may reveal where things are stuck.
(Remember to make more than one snapshot of each thing, as per the instructions.)