In Settings, if you go into Post Customization, the Default sort for Posts, at the top, is for your feed. A bit further down, the Sticky sort per community setting can also be set for specific communities and overrides the upper setting. That second setting does come up if you search "sort" but the first doesn't. Some of the settings seem to be unlabelled and does not come up in search.

Regarding the reset of your settings, that does seem odd. If other people have experienced this as well, hopefully they'll chime in with their experience. I've had this happen way back but haven't noticed this recently.