I had the Exynos version. Same issues with GSM signal and call issues. Display looked washed out and discoloured. Battery life was abyzmal.
I've now imported the N9860 Hong Kong Snapdragon version and it's a completely different phone. It's fast as hell, battery is great and the display is bright and vibrant. It also doesn't drop calls. Only restriction is that Samsung Pay is region blocked but I use Google Pay anyway.
Honestly it's a copletely different phone and was only £800 all in. A bit of a bargain considering Samsung still want £1179 for the really really inferior UK Exynos version.
Did you try the options I mentioned in wee-update.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help.