It's possibly a bug.
But...why are you changing your sequence resolution so frequently? Ideally that would be a rare ocurrance.
It is a rare occurrence after getting going, but a common part of the project set up (e.g. resizing from 4000x3000 GoPro timelapse images). So I basically have to restart Premiere multiple times each time I start a new project.
Do you get this same problem if you create a new sequence with the desired frame size and then drop clips into that empty sequence?
Resizing the sequence always warns me that it will reset clip previews even when I have none.
Yes, Premiere has done that for as long as I have been working with it. It's kind of a last chance to not mess yourself up if you have invested a lot of time in previews.
a common part of the project set up
Set it up correctly the first time to avoid the bug.