Hi hajdusz,
is there any specific reason that you need 19.4R1 on your EX switch? Please note that latest and greatest JUNOS release are the most unstable release as well. The currently recommended release for EX4300 is Junos 18.1R3-S8/18.4R2-S2 (updated on Dec 10th). Please see the following link for the recommended releases:
https://kb.juniper.net/InfoCenter/index?page=content&id=KB21476
If you don't need any specific feature, and if stability is important for you, I'd suggest to downgrade to 18.1R3-S8 or 18.4R3 and then check again if your issue is solved or not.