Perhaps one out of 10 QSO exhibit WSJT-x lagging a response from the other guy, by a cycle. Frequently, it's during an exchange of repeats of R-nn / RR73, when it seems the other station is not responding, and then two cycles of responses "pop" into the Rx Frequency window at once. PC is running cool (5-15% CPU, no memory shortage...). Windows 10-64, running WSJT-X 2.5.4
73 - Mike - K1VI