There are a number of slightly conflicting favicon standards and each system works a slightly different way. Having done searches at various times for reliable generators, I never found a good one until I accidentally saw an excellent one linked from an SO answer. It handles all the formats, and can check which systems will accept the favicons found at a particular site.
I’m just writing this to bring attention to it. Definitely worth a bookmark.
Favicon Generator for all platforms: https://realfavicongenerator.net/