What you are experiencing is most likely the "height-bug" that many Oculus Rift users have been experiencing (me as well). Oculus has an update that is slated for release this month that will hopefully address this issue. For now, we have to live with it. You can try doing the front-facing two-sensor setup, as that has shown to be more stable and less likely to have the height bug occur (at least for me), but when you're doing 360 degree setups, if the height bug is there, its there until Oculus fixes it.
If you are using SteamVR, I would recommend installing "OpenVR Advanced Settings" as it will give you the option of setting your floor height while in game, so when this glitch does occur, you can always pause the game and reset the floor, without having to exit and redo sensor tracking.
PC Specs:
Intel i7-6700k @ 4.5 Ghz
Gigabyte Z170X-Gaming 3 Motherboard
RTX 2080 Ti - MSI VENTUS
16 GB CAS-10 RAM @ 2400 MHz
Startech 4-port/4-USB controller add-on card
850W Corsair HX850 PSU
4-Sensor, Roomscale Setup