Here's a thread where I walk through our hassle trying to get Gsuite support to try to acknowledge they even consider this an issue, let alone do something about it: https://twitter.com/JustinMcCammon/status/141761476919279206...
tldr; remove all bit.ly links from your emails
Google has massively messed up spam filters and we got confirmation that they are aware of the issue from Gsuite support (although it seemed like Google did not consider it a problem and was just the absolute worst to try to work with via support. Absolutely terrible at every interaction except one rep who had to fight the system to help us investigate).
We use Gsuite at work and ran into issues where in the middle of an email thread, with contacts we'd exchanged dozens of messages over many weeks and even months, suddenly the emails were being sent to our spam folder or worse, rejected entirely (which ends up being a silent failure unless you are really on top of your email logs or you have clients that pick up the phone and say "why haven't you responded to my email?" we had the latter).
We reach out and spent weeks going back and forth daily with Google "support". I'd spend hours on the phone with them going through steps to recreate it and trying to find workarounds. Aside from one good rep who acknowledged many other people were writing in about it at the same time we were it really seemed like Google could not care less.
At one point I got so desperate I searched on twitter to find other people complaining about things. I found a person who was willing to help me - she was on the other side of things - someone NOT using gmail trying to send emails to gmail users and getting the rejection bouncebacks all of a sudden. She helped me figure out some of the root causes. Turns out Google decided that all bit.ly links were bad and if one appeared in your email it was either rejected or sent to spam (we couldn't figure out why one or the other). With her help we figured out clear steps to reproduce the issue and I did so on emails I controlled to send all the email headers and such to Google thinking they would realize the obvious issue.
Turns out we had bit.ly links in our own company email signature and so what was happening is when a client would reply to our email and it would include our own signature in it then google would flag that email as bad.
In addition there were some cases where links to google docs or youtube (the irony!) were also getting flagged.
The only thing we did that worked was to set up custom exception rules in gsuite to always allow emails through that contained bit.ly links or gdoc links as well as turn off ALL spam filtering. Naturally we all got lots more spam but we also could get regular emails again, which was much appreciated.
I had a phone convo with someone at bit.ly since I figured they might like to know and maybe could apply some pressure to google but after running it up the ladder there they ghosted me.