I don't think it's related to our CFW's tho...
Since Gingerbread email auto-sync not working - Android Forums at AndroidCentral.com
I tested both firmwares again to determine when the sync stops working.
For the AllDro2 firmware, it stops working in less than 6 hours.
For the Tsunami firmware, it stops working between 27 and 33 hours in my first test. Within a day, the sync works perfectly (manually too).
I will try the 0.2 version of the Tsunami once Steev releases it.