That all points to it being a cache issue. These are the temp files saved in memory. They need to be forced clean.
Or you can simple stay with another browser that you like. I'm sure they would offer features that would be an improvement over the factory Apple Safari browser anyway.
Once happy with the alternate browser you can set it to be default (sort of). https://discussions.apple.com/thread/8317628
Anyway, at least you now have the answer.
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