Not all recurring jobs trigger when they should

I have scheduled a lot of recurring jobs - 679 to be exact. Everything used to be OK, but lately some of them just fail to schedule at the specific time they should. I have been using Hangfire for months, without much issues, so I'm sure that the CRON expressions are correct, and the setup of the server is working.
Can be the problem that the recurring jobs are too many and the scheduler can't handle them?
If I trigger them manually, they all work just fine, problem is they are not scheduled automatically.