I hope you're well today. I do have some information about the missing customers and payees in the bank feeds.
If you're referring to those that are still on the process of being categorised, the payee or customers might not appear at all. This is normal since QuickBooks Online depends on what was being sent from the bank.
However, are the payees or customers not appearing on the Supplier/Customer drop-down menu? This can be a case of a cache-related issue.
You'll want to rule this out by using an incognito or private browser (good for spotting webpage issues). You can use these shortcut keys:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari (new versions): Command + Option + P
Log in to your QuickBooks account from there and check the list in the Supplier/Customer drop-down menu. If all customers or payee appear, you'll want to go back to the regular browser and clear the cache.
Close out your browser processes after clearing the cache. This will apply the changes made to the cache storage. You can also use another supported browser.
If you're ready to categorise your bank transactions again and do your reconciliation routine, you can check these articles: