Why does xdebug fall off? How to fix?

[evgeny-2019]

In php.ini I set the following values:

max_execution_time      = 0
max_input_time          = -1

I put a breakpoint. I open the page. The page loads within 2 minutes. Then I get a 503 error:

Service Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

This prevents me from debugging the code. How do I fix this?