Hi Adji,
From Track View, I went to a Synth Instrument track and I ciicked, just once, on the Freeze Synth button. It froze the track straight away. No issues.
I also froze some more Synths by clicking on the Freeze Synth button in the Synth Rack.
This is in a project with over twenty synth instances in and a load of effects plugs.
Not exactly what you wanted to hear I guess...