This:
Player701 wrote:It appears that the floor of sector 195, which is triggered to lower when the switch is pressed, doesn't stop where it has to and continues lowering towards negative infinity.
The sector in question is quite unusual in structure. It consists of 4 unconnected linedefs and effectively has an area of 0. All of these linedefs are self-referencing (both on front and back sides). This sector is triggered by a switch with an "S1 Floor Lower to 8 above Highest Floor" special, and I guess the problem lies in the inability to find this "highest floor" because sector 195 doesn't reference any other sectors. This behavior is not unique to GZDoom, and has been found to also occur in PrBoom-Plus.