Gareth - Just saying - Same thing happened to me 8/5/18 when I factory reset my Nexus 6p which is no longer in the Beta program.
I've uninstalled/reinstalled - no success - still stuck on the Just a Sec.
Same thing happened to me and my now "old" Nexus 6p when I did a factory reset 8/5/18. I am not in the Beta program now - phone too old.
Any suggestions?