Updated targetSdk, but some users still get "app isn't available … older version" (in Closed Testing)

My app aged, I didn't notice the warnings, Play Store now says "App not available" for anybody on Android ≥15.

bumped targetSdk 34→35
minSdk 24, compileSdk 35, FWIW rebuilt, created new release in Closed Testing track Tester A + Tester B both added to Testers list both accepted "Beta Tester" (and have waited not only " both see "App name (Beta)" in the Play Store app both have Android 16 But Tester A can update/install Tester B can not:

This app isn't available for your device because it was made for an older version of Android

Notable differences, as far as I can tell

Tester A has had the app installed before (an older version on a different device) for Tester B this would be a "fresh" install

Why does this happen, and is it fixable? Sounds like this bug, but wouldn't it affect both testers?