Hello Lie, sorry to hear you pain, it’s not nice.
Which instances of jisti did you use? just for the sake of knowing. honestly I have never used the ones referenced here with many people. ugne told me the other day that the komuniki one worked well with 5 people.
the difference with Jitsi is that it’s not a company offering a service. it’s an open source software. so depending on the instance of Jitsi you use, you will have more or less computer power (CPU) on the server that is hosting you. it also depends on the amount of people using it at that exact time of your call.