This seems to be the problem here - the multis that you are using are probably built for studio work, where you can render or freeze instruments if they become too memory-hungry. Trying to have a number of them instantly available for live work is a pretty big challenge.
Building a live set requires a different approach - managing the available resources to optimize latency, avoid drop-outs and minimize switching times. This means that you’ll have to cram a lot into your available RAM; some re-building of your setups for live use is probably unavoidable (unless you have unlimited RAM and processing power).
But let me suggest an alternative way to address your issues with sample-based instruments and Kontakt instances, which is to differentiate between the actual sample sets and their processing afterwards. Let me give you an example:
In my main piano rack, I use XLN Audio Addictive keys as my main piano. I use only one sample set with it (a studio grand without any effects or EQings added), which is loaded with the rack and never changed. But I have a powerful effects chain after it (compressor, chorus, EQ, delay, reverb), which allows me to create numerous differen piano rack patches from this same piano sound without ever having to change the sample set, simply by changing effects setting in the processing chain.
So maybe, you can reduce your live setup to a set of very few large sample sets that stay static and change their sounds by adding flexible effects processing, which can be re-configured easily. If there are some smaller song-specific samples, you can easily load those between songs via “whole bank” state behavior in Kontakt, but as long as your large sample sets stay constant, you’ll be in good shape.
But yes, this means that you’ll have to re-work your sounds - you can’t simply slap your favorite Kontakt multis together. But as I mentioned: a live VST rig is a completely different beast than your usual studio setup; investing some time to build something that works for the rigours of live work will pay back on stage! Put together something robust and easy-to manage - this will give you more peace of mind and make you enjoy playing music instead of dealing with loading times and quirky performance
And TBH: I don’t think you need such a differentiated sound palette for live use as you would want to have in your studio. Yes, I have about 10 great piano sample libraries for the occasion when I want to find just the right one for a song I’m creating - but for stage use, I’m perfectly fine with my Addictive Keys grand piano and about 10 different Comp-EQ-Chorus settings and song-specific flavoring of reverb and/or delay. Simplify, simplify…