I believe it could be your phone's network configuration is out of date, as Maxis quite often reconfigure their network.....
Thus, assuming you're still able to make calls and receive SMSes, you could try the following...
1. Get Maxis to send out an SMS (to your phone number) that will help reconfigure your phone (Pixel 2 XL) to receive signal on their network.
2. Call the Maxis service personnel guided you to manually reconfigure the network connection settings in your phone.
I used to face the same issue like yours as well, thus doing the above 2 have helped solved my data issue.
I hope this works out for you.
Maxis no mobile interne, can't figure out the cause!