VSTi's going silent when I change selected tracks

If I have my session playing, with a VSTi track selected, when I then change to another track, the VSTi that was previously selected will stop playing. To get it to re-start, I have to open the VSTi, switch off and then back on again. Very irritating! Anybody got any possible solutions or trouble shooting ideas?

I’ve had this issue occasionally over the years and never looked into it but at the moment it is happening constantly and it’s driving me mad.