I'm a member of global entry and nexus. I never have an issue getting flagged just OLCI doesn't work. Kiosks always work even when OLCI fails - normally if you are DHS flagged kiosks won't work either.

BTW. I do recall US to UK worked with OLCI last time. I have a UK Passport so assuming it's proof of onward travel/docs when not on a US passport or a Passport issued by the destination country.

Eg. Japan, Taiwan, Korea, Australia seem to stop OLCI for me. More of the issue for me is asking me for resident card info but not actually doing anything with it - like the check in process programming was never bug tested and actually works for anyone returning to the US.