Strange characters are displayed in the display of a VT7000 and SE7000 Series thermostat.
VT7000 Series and SE7000 Series thermostats
The thermostat has experienced a brownout condition. Any time the power drops below 16-17Vac for a 1/10 of a second or so it will cause this condition.
The thermostat still updates to the BMS correctly; it’s only its display that’s affected.
Cycling power to the unit will clear the issue. However, if the brown out condition is not addressed, it can happen again. If a repeated brownout issue at the site cannot be corrected, consider powering the controller with an UPS.