Gmail sync issues with my Droid Turbo 2 on 5.1.1

Hey everyone. As I mentioned, I have a Droid Turbo 2 running 5.1.1 on Verizon. Unrooted, locked, etc.

Recently, like maybe within the last week or two, Gmail has just sort of stopped syncing. Used to, I would get notifications for emails as they come. Email comes in at 2:34, I get a notification at 2:34.

Now, this doesn't happen anymore. I go to work and come home with no notifications nor unread counts on my Gmail icon. But when I open my laptop, I'll have multiple unread emails waiting for me. If I open the Gmail app and manually refresh, they all appear. Once I've manually refreshed, they usually continue to come in regularly for a few hours. And then they stop again.

This holds true for all of the email accounts I have through Gmail which is 3 total. I also have a work email through the Outlook app, but that gets emails synced and pushes notifications no problem, so this is solely a Gmail issue.

Syncing is enabled for them in the settings and is set to sync the last 30 days. I am only using a primary inbox for all of them, so it's not that emails are going under other labels and I'm not being notified about them or anything like that.

I really have no clue what could be going wrong, but I'd like to be able to receive my emails as they come in again. I'm going to try downloading and setting up Inbox in the hopes that it might solve things. Unfortunately, it's hard to know if anything has worked until after I go to work and come back to find out if I've missed anything.

Edit: Turns out one of my emails isn't set configured to be used my Inbox yet. But if it solves it for at least one email then that's a good step.

If anyone has any ideas as to how to fix this, I'd appreciate some input.

I can provide screenshots and such as necessary.