Those “shark bite” fittings wear out over time. Haven’t had a problem yet with mine on this unit but I’ve used them for projects in the past and they were on my consumables list for the month.
When you press the line in hard does it click? Can you pull the line out with ease after you insert it, without depressing the ring?
If it just goes in and out you need to replace it imo if it clicks in when you try to re-isert it and you can’t pull it out w.o pressing in that ring then I’d say it just either came loose or wasn’t inserted properly at first and should work fine now