I know I'm bumping an old thread. This behavior happens to me all the time (a few times a day). I haven't been able to figure it out. I don't use fish shell, but rather bash. I do use a multi-monitor setup but I think I've seen it when only using my laptop alone. It probably dates back to High Sierra. My typical use case is "mate ." in a directory, not a specific file. That directory will have a ".tm_properties" file making it a project. I use iTerm2.
So TextMate is running, I switch to a directory in iTerm2, type "mate ." then the command just hangs for 5-10 seconds before TextMate finally comes to the front.
The laptop has an SSD. I think the problem is worse when I have a USB drive attached for Time Machine.
I haven't thought to try clicking TextMate in the dock or command-tab switching to it. I will try that next time this occurs.
I assume the folks who were suffering from this problem in this thread have continued to put up with it? I know how frustrating it is. :-(