Do both channels do this or just one? If your using channel 1 of Z-4000, try channel 2. If both are jumping, you need to find out why. 30V is high and something is wrong. Not sure this is a house thing unless your seeing you lighting go bright too.
PS-1 should not hurt system. Normally folks use var channel for running conventional. Otherwise you are using the Z to regulate power via Fix channels.
Are you sure you do not have a phasing issue in your layout where you are some how out of phase and as the train cross the intersection it is bridging out of phase voltage causing the spike. The burned up Diodes are the spike suppression TVS. So there is a problem. You need to isolate to figure it out.
Run your conventional eng without TIU and just Z-4000. Does it spike? Build a single smaller loop on the floor, try conventional no tiu with Z-4000. If it still spikes, Z-4000 may be the issue. If it does not, look closer at your layout.
If you have one loop on one channel red to center rail and some how the other loop on channel 2 black to center, and the train transisitoned across you would have a good voltage spike that the meter may be reading and blowing TIU components. G
My layout is pretty simple. Double loop with crossovers that are isolated at the joint. One track on fixed channel 1, the other on fixed channel 2. One lever to each input. Red to center on both, black to outer. The spikes I only noticed when the Z4000 was at idle, meaning no power applied to either track.
I do not know if these spikes have occurred while powering either track, but the idle spikes have merely made me suspicious.
The 30 is a shot in the dark guess based on what can barely be made out in half a second.
I should also mention, the second TIU failed during a thunderstorm and I was without a surge protector at that time. I was in the basement with the train’s sounds on and did not realize it was storming. After that, I promptly bought a surge protector. Is it possible that damaged the Z4000? The house lights did not get any brighter or dimmer during that time, nor do they normally.