Ah, that sucks. Never played EU4 except the initial demo, was always more interested in CK2. My management of finances in EU3 was similiar, at the time, to my management of my own personal finances at university - poor
For a game with so much scope/big playerbase, you'd imagine they'd get the hotjoin fixed.
I'd definitely recommend a return to Stellaris if you get a chance, but as I'm also never really a big MP player, might be that it suits SP more... would you recommend EU4 for singleplayer alone?