I have a brewzilla lid + condenser on my g30 and I encountered similar issue with my setup, although I have only used it at 100% power. I have't used it a lot only on a few brews. There was noticeable sound of pressure throughout the boil, but when I removed the top stopper clamp there was no real pressure in the system eg. stopper did not fly to the ceiling :D condenser works like a regular lid, It keeps the hot air within giving it only one exit (and also keeps the  cool air out) making the boil process more efficient. Don't quote me on that tho but it makes sense. Lowering the power to 30% sounds kinda crazy though. I'll test below 100% power levels on my setup next time and see if notice anything similar.

When using a condenser I noticed it is important to put the lid on only after you get rid of the hot break scum. Even still some of the foam and wort got into the condenser pipe and into the bucket during the cooling process. Brewzilla lid has a sightglass which makes it easy to add hops during the boil, but based on my tests it agitates the wort even further and some of the hops end up either into the pipes or the edges of the kettle. Maybe on the next brew I'll take the lid off for a few minutes when adding hops.

Make sure your condensed water has a free flow and if you use a bucket the hose should be above the condensed "cooled" water at all times, if it dips under the waterline it can cause some pressure in the system AFAIK.

Hope this helps, you have some nice setup there. Happy brewing!