I would lower the max.threads on your mid servers to around 75 and test.   This can be done under Configuration Parameters on your mid server in the GUI.   For the new number to go into affect, you would need to restart the mid server service.       Also, did you validate that your mid servers upgraded to the new version?   Also, depending on your VM configuration hosting your mid server, you should also consider going to the conf/wrapper-override.conf file and remove the "#" off the setting:   wrapper.java.maxmemory=1024.   restart the mid server service after making this change.     Assumption is that your VM is 64-bit.