I'm having the same problem shortly after my update. My data Connection bounces around from LTE to nothing at all and also 3G. It does that about every 5 or 10 minutes and i constantly have to restart my phone then turn Airplane mode on then off until it comes back on. Also when i have LTE it'll say can't connect to server or server not resounding. It's very frustrating
Which Android 9 build do you have? DSC1 or DSD3? When did you updated like a month ago or recently? I had the same issue with build DSC1 but the new update DSD3 which came out this passed weekend fixed the issue.