You may be forgiven for thinking that after doing a massive item level squish twice before, World of Warcraft’s developers would have learned how to do so without causing major disruptions to the status quo. You may also be forgiven for having a moment of blinking confusion at the concept of twice before there. But no, it turns out that people are still having problems with the new level squish, specifically with soloing Legion endgame content once the item level and actual level squish are implemented in the current test realm.
The bright side is that director Ion Hazzikostas has gone on the record saying that this is unintentional and tuning is still being finished; when the pre-patch is actually live, all of the stuff you can solo now should still be possible to solo. The down side, as noted by the first commenter on the Wowhead article, is that based on the aforementioned prior two instances of this, there will still be issues with scaling for a while as everything gets sorted out. So if you have some appearances you want to farm for, maybe you should do that now rather than waiting for the pre-patch.