I did a bit of digging here and internally and have seen some reference to modifying settings with page rules, but don’t see anything in docs that helped and the options I saw were not granular, only on/off.
Regarding connection, you should run a trace from on of the affected machines. From a terminal window,
$ traceroute example.com if they don’t have terminal access, have them go to https://www.example.com/cdn-cgi/trace. If you’re having issues, it would be good to include the output of that if/when Support asks. To contact Cloudflare Customer Support, login & go to https://dash.cloudflare.com/?account=support and select get more help. Please give Support the complete details and link to your Community post. And, share your ticket number here and I’ll keep an eye out.