Error: "We stopped hearing from agent Hosted Agent."

This is a build for Dynamics 365 Finance and Operations. Hosted classic pipeline, ran fine for weeks, but all of a sudden I get this error.
Already increased the timeouts where I could find any.
It appears to conk out each time at 1 hour and 15 minutes, which tells me that it must be either a parameter or a limitation, but I can't find anything.
The timeout happens during the X++ compile process.
I've run this same pipeline config for other customers with much large code bases without problems, and I'm stumped as to what the cause could be.

I found this in the documentation:

Private project: One free parallel job that can run for up to 60 minutes each time, until you've used 1,800 minutes (30 hours) per month. You can pay for additional capacity per parallel job. Paid parallel jobs remove the monthly time limit and allow you to run each job for up to 360 minutes (6 hours). Buy Microsoft-hosted parallel jobs.

But from what I can see we have not hit those limits. I don't run parallel jobs. However if the 60 min limit also applies to single-threaded jobs, maybe that is the issue?

Any ideas? Any additional detail I need to provide?

Ignore the word "parallel". It's just indicating that jobs can run in parallel if you pay them for additional capacity. If you only have a single "parallel job", there's not really any parallelism available.

On the hosted agent at the free tier, a single job is limited to 60 minutes and will be cancelled after 60 minutes have elapsed. The solution is to either host your own agent or pay Microsoft.