After trying to contact Clara.io via several emails (ignored) and YouTube messages (disappeared - marked as spam?), I've come to the conclusion that Clara.io is heavily throttled for Basic plan (free) users. It's my opinion that they're being dishonest by failing to disclose in their plan details that on the "Basic" (free) plan, after a while, changes to your models won't save, imports will time out (won't work), etc.
If they throttle/limit the free ("Basic") plan more than they state in the plan description (at https://clara.io/settings/billing), they should be open and honest about it.
I was going to subscribe to their Standard plan, but why would I? If they're dishonest about the Basic plan, why isn't this going to apply to their Standard (their cheaper paid-for plan) too? When will I get problems with the Standard plan that would then require me to sign up to the $100/month "Advanced" plan? (And even with the $100/month plan, by the way, you still only get "Support via public forum" !!! - Yes, your only support is via this virtually completely dead forum.)
MY ADVICE: FORGET CLARA.IO! RUN AWAY FROM IT AS FAST AS YOU CAN!
IT APPEARS THEY'VE MOVED ON FROM CLARA (their focus is on threekit) AND SO SHOULD WE.