Attendance isn't just low before the summer break, it's low all the time. MEPs miss votes for reasons as trivial as there being a football game on, because why not? It's not like their votes matter much anyway. Everything important is decided upon long before they get involved, they aren't allowed to actually write laws or pass them or repeal them, and so nobody with any political ambition goes there unless they're using it as a springboard to national politics.
https://www.youtube.com/watch?v=166SAhPB5-Q
> "Mr President, our parliament in the United Kingdom sat for 142 days last year and it was criticized widely for only sitting for that amount of time yet we in Brussels and Strasburg in the plenary and mini plenary, we sit for just five days a month and on three of those days it's only part of a day that we actually sit for. So we end up with debate in this chamber where microphones of speakers are cut off after 60 seconds, 90 seconds or 2 minutes, and we have no way of expanding on a point, we have no way of properly challenging a speaker, we have no means of proper scrutiny of proposed legislation that comes through. Surely it would make more sense to have sufficient time allocated to proper debate to reason debate and those who actually believe in the structures and institutions of this place should surely welcome that. I think my 60 seconds is up."
You can tell it's a joke institution because they regularly penalize MEPs for the content of their two minute speeches. Britain has the concept of parliamentary immunity but the EU does not, so you get "politicians" who are told what they can and cannot say by the leaders of other parties.