I had similar problems with the MTH wifi DCS Explorer from last year for my Christmas layout. I didn't dig very much, but I suspect the problem is that the DCS system is a WiFi access point, and it's not a very good one. If it's nearby another WiFi access point, or in range of a lot of them (typical urban/suburban environment), it's not going to behave very well. I can't remember if you can switch to it connecting to another WiFi AP instead of being its own AP, but that could help as it reduces congestion. Also, I think the software can be updated, which is another way to try to reduce problems. The goal would be to reduce WiFi congestion as much as possible near the layout, and try to force the MTH system onto channel 1 or 11 which should have the least congestion, but that's a guess. You can get phone apps to help you determine which WiFi channels would be the least congested, but they tend to cost money. However, given how much you can spend on MTH and Lionel, it's closer to a small drop in the bucket in the long run. If it helps make your system more stable, it's pry worth it. Finally, turn off the house WiFi as a last ditch effort to help reduce congestion.
Note, these are guesses. My chosen vocation tends to give me access to a lot of how WiFi works at the detail level, so I know a bit about how to deal with issues. But I honestly didn't spend a lot of time trying to determine why it was having more troubles than it maybe should have. There are lots of potential reasons that can cause issues. Another would be weak track connections which I found caused the MTH system a lot of trouble. Sometimes while running, it would just "lose" a train until I cleaned and tried to reseat the track section. I was using Fastrack.
That said, I got frustrated with it, so I'm switching to DCC with a wired ring bus connection to each track section despite the effort and costs. It annoys me that the DCS system has restrictions until you buy the expensive gear (Explorer hides sounds and lights while the full system doesn't), and it's just not as reliable as I need it to be, even for my smaller layout. I'm in the middle of rebuilding the layout, so I haven't tried it yet, but I should be setup in the next few weeks to a month. Hopefully DCC just works better.