I'm using a Pixel 2 XL and using the standard Gmail app from the Play Store. https://play.google.com/store/apps/details?id=com.google.android.gm
I'm rooted but not doing anything to the Gmail app and no global ad blocker. I do block ads in Firefox but that's different.
Oh I definitely did, using this release but no dice. :(
Coincidentally (/s) Spark released their Android app today. It's not quite Inbox, but it's still a thousand times better than Gmail. I refuse to use Gmail, Google can go f$&# itself.
First, try and FIND the messages. Log into your account using the Gmail web interface: https://mail.google.com/
Have you checked all the Inbox tabs (if you have them enabled): Primary, Social, Promotions, Updates, and Forums?
Have you looked in the “All Mail” label for the missing messages? What about “Trash” (or “Bin”, but not “[imap]/Trash” or anything else)? What about “Spam” (but not “Junk” or anything else)? Be sure to look past the first page if the messages you’re looking for are older.
Have you used the Search Mail function (with the term “in:anywhere”) at the top of the page to look for the missing messages?