Reaper hanging temporally when approaching end of time selection?

[Ideosound]

Hi, sometimes I get odd behaviour in Mojave when I have a time selection enabled. If I don't have loop on, Reaper hang's for a few seconds just before the end of the time selection, then comes back to life about 10 secs later after the spinning colour wheel. If loop is on, it works (loops) fine. Anyone had this before? Is it a buffer issue? it might be a plugin also?

I'm a few versions behind the latest release.