Don’t take this the wrong way MRK, but I’m glad someone else is having this problem! 
My setup is:
I’ve got LG B7 <–(arc)—> Marantz Nr1607 <-------Vero 4K
…and I have exactly the same issue as you. I had a short chat about it on this thread:
My case is the same weirdness as yours - sometimes I’ll be watching something on the Vero, switch off for the night. Wake up next day and the kids switch the TV on for Netflix and ARC won’t work. I’ve tried a bunch of stuff and it’s definitely the Vero, and the fix is to pull the HDMI cable out and ARC reestablishes itself. Powering the Vero off does work sometimes, although there tends to be a 5-6 second delay while the AVR sorts itself out.
My CEC adapter is off, and always has been (I use a Harmony for all the device controlling), so I don’t think this is the cause of it.
For me, it’s very intermittent and hard to reproduce. After the suggestion on the thread above, I switched the HDMI cable out for an Amazon basics one and I haven’t had the problem since (I was using a freebie cable that Peter Tyson sent with the AVR, although it did look like a nice one). It’s only been a month since I did that though and sometimes I don’t encounter the problem for weeks at a time so it might not be the answer. I do wonder if it’s a shielding issue.