I've been feeding here since January. I see the same situation with my "Availability" graph also, nearly every day with at least one red gap (see image). But my Raspberry Pi is running solidly and is hard-wired to Ethernet on a very stable high-speed campus network. Like you, my other fed system (FA) does not show any gaps in the same time periods.
For weeks I've noticed my gaps are usually between 5:00-11:00 UTC time, so my educated guess is a server-side load issue that can't always accept incoming data.
I haven't taken the time to dig into the feed script to see if the reliability of reconnections or timeouts might be something we can improve on our end.