One month ago I disconnected power to my Wem3080T meter for about 24 hours.  I did not disconnect the CT's from the meter, or reverse the direction of the CT's.

When I powered up the meter again, ALL of the 3 meters were reading in reverse.  I then reversed the direction of the CT's - TOWARDS the source rather than the load, and all meters were then reading correctly.

Can this behaviour be explained?

Hi:

How are you using the WEM3080T?

Please note that both the CT direction and the voltage input connections can affect the sign of the power reading.

For example, if you connect the neutral line to Ua and the live line of phase A to Un, you may get a negative power reading, even if the CT is correctly oriented.

Or check whether there is "phase mismatch" in installation 

https://www.iammeter.com/newsshow/blog-meter-accuracy#phase-mismatch-in-installation