Can you describe some additional details? This is NOT normal behavior, and something fishy is going on.
1. The settings you're using, particularly Red October mode and any special settings under Options > Audio and Options > Video.
2. Any other things dissimilar between the two installs. Are you using them from different user accounts or anything?
3. Describe the computer hardware you're using briefly (CPU, GPU, RAM, etc).
4. Do you have an Anti-Virus application installed? If so, does disabling it entirely make any difference? How about uninstalling (just as a test, sometimes disabling doesn't really disable all AV behavior)?
First, make sure you are using the most recent version of MC19. This will NOT be the one on the regular JRiver download page, but the one "pinned" to the top of this forum board (currently 19.0.102).
Anti-Virus problems can be quite noodly to figure out. Often they can be mitigated by excluding a few essential MC processes from the "watched processes" and excluding the MC Library location from the "watched folders" from within the AntiVirus application. If you uninstall yours, or disable it, and the problem goes away, then you know what to target.
It is even possible that you already have MC18 excluded, and that's why it is better behaved. Or, perhaps since it is older, your AV application has special things built-in for it, that don't apply to MC19 (which is newer)? Or, maybe there is just some difference in the way it accesses the disk that makes it more problematic with your particular AV application.