I don't use WMP on W10 as it's been problematic from the git-go. avi files are very old movie files (c. 1992). you could try using a different player such as the free VLC player. However, in my experience there are lots of issues with avi files created with older codecs (literally there are hundreds of them to choose from, and often avi files were encoded with more than 1 codec, which means your chance of finding the right player with the correct type and number of codecs is not good (you'd have a better chance of winning the lottery!).
You can also use a free converter which you can google, and simply convert the avi file to a more modern movie file type such as .mp4, or mpeg4, wmv, flv (flash player), or quicktime.
Next question is, are those avi files created by you on a camcorder or smartphone? or did you download them from the Internet? Are they commercial movies like those you'd buy from Netflix or Redbox?
I still have some old avi files that were commercially produced, and trying to make those work on W10 is probably not going to work for you. The conversion process you can do yourself with free software may work on a few of those files, but certainly not all. You could also pay a Service to do the conversion for you, just about every community I've lived in, there is a local person doing this service. They are in the yellow pages or search the Internet. You can find people who do this by looking up someone who converts old VHS tapes onto Digital discs such as CDs or DVDs. They often have the right software on their computers to also convert ancient movie files such as yours.
In the meantime, simply separate all your avi movie files into one folder and get them out of the folder you have your PhotoBase program pointing to. You yourself observed that if the avi files are not sharing the same folder nicely, separating them seems to work. This could be accomplished quite easily with W10 File Explorer using it's file management capabilities. Think of it as having 2 teenager siblings in your house who can't get along living together in the same room-separating them into different rooms or living spaces often solves the problem!
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