question

If they are the batteries that are linked then the bms will fail. Reason mentioned by @klim8skeptic . The FETs inside are not designed for a 48V connection.

Charge total current using the whole system (grid and solar) less than 40A. If you are charging higher than that then the dc ripple will appear in the bms.

If you are using a multiple of the 14.6V per battery, then drop the system total to about 58.4 or 58.2v to hopefully reduce the chance of bms shutdown.

@Abdelmjid

I was having a problem with High DC Ripple on my system as well. I have two 24 volt batteries in series and would start getting errors after bulk charge finished and absorption started. It was effecting my MPII and MPPT behavior. It ended up being one of my batteries getting full before the other and the voltage was spiking, going over 30 volts on the one battery. The MPII would stop the charge, volts would lower 3 or more volts, and the system would try to charge again. With this happening over and over quickly, it caused the ripple error. I found the culprit by setting up a midpoint voltage monitor with my BMV-712 and started logging on the VRM portal. I had checked the two batteries before with a volt meter, but not right when they were close to fully charged during the absorption phase, and didn't catch it for awhile. I ended up lowering my absorption voltage lower (56.2) and it solved the problem. I picked this voltage by looking at the graphs and seeing when the midpoint deviation started to get above 2 percent between the two, and setting the limit going right before that point.

It may be that you have one battery in your set getting fully charged slightly faster than the rest and spiking the voltage.