I tested Workshop5 and Workshop6 and looks they already started running slow for all cores. I was able to get smaller script that have the problem. It do not only happens with multi core. On the script below with 2 cores the walk 1 and walk 2 runned fast. The walk 3 and walk 4 runned slow. The same happened after disabling multi core. I increased the number of cores and the first walk for all cores runned fast and it did make the walk train fast even for 2 cores and for no multi core. The speed up was preserved after a Zorro restart. Commenting out "while(asset(loop("EUR/USD")))" while keeping "EUR/USD" selected did make this code runs slows. However with my script half cores started running fast and half slow.