Exact same issue here.
If I play only desktop for a few weeks, Iβm good.
Only iOS for a while, Iβm good.
Flip flop same week? Permanent store highlight
It can only remember new items by device, so each patch you'll have to clear it once on each device you play on.
Varedis is also right that there are some un-intended oddities around items in bundles causing tab highlights.
It should not always be highlighted though, once you view each tab with new content on each device you use, then it won't be highlighted until there's new content in the store. (Which is typically every 2 to 4 weeks)