Can you post a picture/screenshot of the sense reading where that shows ?
Says a 1000 words.
Are your 2 inverters both connected to breakers at your main panel ?
Or do you have a so called supply-side hookup ?
You mentioned the new inverter is hooked up to sub-panel, so that is load side for sure.
How about your initial inverter ? does it have a dedicated breaker or a fused disconnect ?
reason for asking: Sense tries to automatically determine if you have a supply-side or load-side hookup.
For unknown reasons, for years, it sometimes switches between the 2 modes.
And then you get what you are describing.
Search on this forum “supply side” and you will find many articles where things suddenly changed.
eg: Bug showing zero usage? - #4 by dannyterhaar
It only needs 1 email to support to fix it (if that is what has changed)
Looking forward to more information from your setup.