that's weird, i have done multiple runs concurrently in the past and the times it wasn't working was because of the memory limit on apify side (see image)
btw if it helps, it's still capped at 4 concurrent runs even across multiple actors (when I run 2 separate clay tables that use different actors, its still 4 total)
nope didn't hear anything from them yet - you might want to just try a HTTP API column to run your actor
that will rule out any issue on Clay's side ie if you still get 4 runs using HTTP API the issues is for sure not on Clay's side