Welcome, Colin.
First of all, I have to say the only way to avoid "nasty scares" with any application like this is to make regular backup. What "regular" means is up to you. If you don't mind losing a week's changes, then weekly. If you can only tolerate losing what you did today, then daily. And that backup should be automated. Otherwise, one way or another, sooner or later, you'll be blaming yourself for not making a backup when you should have.
That being said, the first problem doesn't suggest anything is wrong with the data. The program does sometimes have difficulty displaying the information panel. These issues are often fixed by refreshing or changing records, but sometimes require the program be restarted.
Perhaps you know that, and you're associating the second issue with the first because it happens after you've attempted to restart the program. If the program is in serious trouble (and, from your description, it does seem more serious than the display problems I'm used to), it's quite likely it won't be able to close properly. You may need to use Task Manager to terminate the process.
This brings us to the second issue. Given that the program process is still running, this is exactly what should be expected. That process is still maintaining a connection to the database. The embedded version of Firebird doesn't support multiple connections. The error message you get when trying to start another instance of the program means exactly what it says.
This doesn't help much if the problem keeps happening. But maybe it will help you investigate further without fear you're going to lose all you data...After you've properly restarted the program, how long is it before it happens again? Does it only happen on startup? Is it ever
not fixed by terminating the process and then starting the program again?
thought I'd lost it all) but it all came back