You can't be so generic. You have to understand that a video file is not like a .doc or a .xls file. There are many, many codecs and so your problem almost surely depends on codecs used for your files.
I've always used BH, now also on a Solo4K, and it plays every file I've tried so far. In case, it was OBH to have some issues some months ago.
And, above all: I cannot believe that EVERY files of yours have problems, right?
You returned your Solo but it is returning a car because it doesn't like some fuel brand. It was a little bit hasty and drastic. And, in fact, you did not solve.
If you browsed this forum you must've read hundreds of similar complaints if your issue was a general issue and if it depended on Solo4K.