Engine Not on Track
I have been running MTH / DCS 4.2 for years and now 5.0. I have seen this issue with 4.2 and just last week 5.0. I have found out this best solution is to do nothing. Example when it happen last week on the main line, I pick up the locomotive and placed it onto a siding. The next day I came back and the DCS Controller found the loco and I ran the loco again yesterday with, "No Chaos".
This is what works on my layout.