Does it happen with any instrument? If it only happens with specific instrument files, please attach an example. Also, if available, please provide the crash dump from %TEMP%\OpenMPT Crash Files.

Also, you have previously stated that you are using OpenMPT on an external hard drive. Please confirm if you are still doing that, and whether the drive is plugged in when the crash happens. We already explained to you that OpenMPT cannot work reliably when you unplug the drive it is running from (this is an operating system limitation, not a bug in OpenMPT).

I now have OpenMPT installed on my main drive, and this can happen with any instrument.

What kind of formats does the crash happen with? Does it happen with both big and small files? Did it just start happening randomly?
We will need the crash dump that should be found in the location %TEMP%\OpenMPT Crash Files, as otherwise there is no way we can help you. Obviously OpenMPT doesn't crash with all instrument files for other persons.

This can happen with any instrument, and OpenMPT doesn't generate a crash file upon this happening.

Does this only happening when opening instrument files, or also when opening sample files? Does it happen when you drag-and-drop the instrument from Explorer into OpenMPT?

This would happen when I click the Open icon on the instrument page and select and instrument there.

If it doesn't happen when drag-and-dropping the files from Explorer, this confirms my suspicion that you have a buggy shell extension installed. Shell extensions modify the Open and Save As dialogs of any program, and many of them are buggy, causing the application to crash. I would advise you to review the installed applications on your system and check if any of them are shell extensions, or if they install one. A known buggy shell extension belongs to DaemonTools, but there are many others.
Another thing you can try is turning on or off the "Preview samples / instruments in file browser" option in the settings dialog (found in the "Samples" tab).