battery charger

Could it be the cabling to the bttery isn't well connected and the charger is unable to read the true state of the battery?

Could be, depends how its connected.

Multistage smart chargers can be to smart. My projecta often thinks the battery needs to be equalized or reconditioned, this happens because I have a lot of devices in the car drawing backup current, this causes the battery voltage to decay quickly when the charger goes into its monitoring mode after completing charging. The charger sees this as a battery that either requires equalizing or reconditioning.
If I isolate the battery the problem goes away. Projecta are also aware of this idiosyncrasy.

I know the batteries ok so I just turn it off when it happens.

I'm in the same boat as HKB above. I have five 100Ah AGM/gel batteries with known history that all pass normal charge/rest/measured-discharge cycles. My 15A Projecta consistently claims three of them require reconditioning due to the voltage dropping to/below 13v3 during the 90 second (?) end-of-boost rest/test period. It has got to the point where I charge those ones using it as a regulated 13v8 power supply.

I have the Projecta accessory digital readout "remote head" which displays current/voltage so I can see what is going on. Whether the Projecta test is actually a reasonable one is open to debate, and I have discussed this at some length with a (now former) Projecta engineer..

The other issue with their 15A units is the provided leads. They are a bit lean. I understand the 25A units use four-wire connection (*) to eliminate volt drop entering the equation. Those factory 15A leads should NOT be extended, if you want more length a larger gauge cable is really necessary.

(*) four-wire connection uses a second pair of conductors to measure the voltage at the load independent of voltage drop in the leads under load.