I had this before, and started running predictive songs (7 at a time).
I haven’t had an issue for a while until I was just going through the song list(150 songs in our repertoire), testing Bandhelper, was communicating with GP, when the 'Resources running low error came up. I have an M1 MBPro 8GB unit. The memorallocation in the window was 15.8x GB.
Any advice on how to reduce this, and stop it from happening again?
Only option is that my MB PRo is zapped and I upgrade under 3rd party wty?
Can you upgrade the memory?
Unfortunately all Silicon based Macbooks can’t be upgraded (Not easilly) without replacing the SSD and Processor. That’s the trade off for Faster Speed and Better Power consumption. 
I don’t know what plugins you’re using and how many of them require samples as opposed to being physical modeled. That said, 8Gb isn’t that much and macOS needs some of it as well. While predictive loading can reduce how much RAM is needed, it won’t help you if even the smaller number of rackspaces you load still have plugins that require a lot of memory.
If some of your plugins need Rosetta, that will take even more.