I have tried to replicate the reported scenario in Pega 7.2.2, issue is replicable in house if we open the tracer from action -> Trace , however the main tracer is working fine. Please confirm us in which scenario you are facing problem. I will do more investigate on this and get back to you.
When writing the steps to reproduce this behavior I noticed that this time I could save the trace file. Instead, I could not see the content of the primary page in the tracer. When opening the trace in the Pega Trace Viewer, I can see the content of the primary page. Do you have any idea what is going on here? Is this server or client related?