I got a couple of casio watches from Amazon years back. Then I brought one in a physical watch store and realized that all the watches purchased through Amazon were fakes. Especially the strap is so much better on the real thing.
Guide.Zenn22.Shop (redirects to a steam site I think). He has many modded F91W's on eBay.
I have one "fake" F91W, it's actally SKMEI branded and keeps fine time. Not sure I believe his claim that the fakes are so inaccurate, but maybe.
That's a very common problem on the inexpensive Casios. When it happened to my watch I found that new watch cost less than a new strap.