Issues with plugins

Sorry if this is answered elsewhere. I’ve looked. New to computers and recording.
I’m using Cubase elements and a focusrite interface.
My issue is when recording I’ve recorded a second guitar track (drum, bass and guitar already done) and saved it and it was fine. Today I’ve loaded it and it won’t play. Just stutters and stops along. I’m using the hefty STL tones will Putney plug in. If I bypass the plugin and have the track 2 dry it’s fine. I’ve changed the buffer size and that didn’t help. Weirdly, it is also affected when I mute any channel. It stutters again. A friend suggested I need to find out how to record the amp on the audio file as opposed to just pressing record and being able to change amp models after.
Sorry if this makes zero sense. New to it all.

Hi and welcome,

Try to increase your Audio Device Buffer Size, please.