Betreff: ACX2100 - JunOS dropping all network packets after upgrade to version 20
please bear in mind that newest means always most unstable. That's why every release gets maintenance ("R") and service ("S") releases to fix these bugs. That a JUNOS release crashes regularly should not happen of course, but software issues can always happen. If you have an active service contract, you can always open a JTAC request to fix this behavior.
If you are not bound to a specific new feature or a specific bugfix in any release, I can just highly recommend you to use a JUNOS release which has at least an "R3" inside the name. Personally I would not go newer than 18.4 currently without any specific need.