Last purchased Eufy Cam 2C with different system version of all others installed 2C cams

I’ve got two Eufy cam2c kits and after few weeks one more cam last year.
All them has System version 1.7.4 (2021-04-27 last update) and Subsystem version 1.0.91-20210303.
All worked fine.
Than I purchased and added another Eufy Cam 2C (NOT PRO) and added to Base without problem BUT Motion Detection is unpredictable.
Sometimes works , sometime doesn’t work, on the opposite of ALL other cams installed.
The difference is the System version 5.2.7 (2021-04-09) ; Subsystem version is the same of all other cams 1.0.91-20210303.
What’s the difference between the cams?
I hope that an answer exists to explain this strange fact.
Now I am quite disappointed and I am not confident to add more cams.

Thank you and kind regards.