NI 9232 module is not synchronous on cDAQ 9178 chassis

I am testing a cDAQ 9178 chassis with some NI 9229, 9234 and 9232 modules by connecting them to the same sensor (accelerometer) and tapping it. Only one IEPE current is being supplied by one 9234 module, the others are measuring voltage. The modules are being plugged into the same chassis, so should synchronise automatically. I am not using addTriggerConnection or similar to force synchronisation - I tried that and it will not let me because the modules are on the same 'device'.

I am using the data acquisition toolbox.

The synchronisation works with the 9234 and 9229 modules. However, the 9232 modules are consistently about 12 samples ahead. That is, a spike appears 12 samples earlier in a time plot. This is also consistent over different sample rates, from 2 kHz to 50 kHz. So for lower sample rates the time error is larger. It is a similar offset on the two 9232 modules I have.

Any idea what is going on? Or how to fix it?