Online disconnects in Horizon 3

I’ve been playing H3 for a relatively short time but every (I really do mean every) time I try any of the online features I get disconnected after no
more than 15 minutes. I seem to join and sync OK, wait or drive to the next event OK, start and finish the event OK but often as soon as I finish getting any achieved rewards, credits ect, I’m disconnected and sent back to solo.

I have done a complete hard reset of my Xbone S, my NAT is open, I have very good download/upload speeds being on a cable ISP (in the UK) and hardwire connection to the Xbox and just to be sure I have carried out a full reset of the modem despite having no online gaming issuse with any other game I play with the exception of Horizon 3.

Any reasonable solutions and or suggestions will welcome and appreciated.

I have raised this in the support threads but so far no advice so I was hoping I might reach a larger audience here … here’s hoping and thanks in advance.