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