JasonC

Was the 1st picture of the battery stats taken at the same time? If you look at the picture you will note that the batteries are at different voltages which is odd for a parallel connection.
Does any of the cells ever reach 3.65V during charging which will trigger the OVP? This might explain the different pack voltages in the 1st picture showing battery stats.
This might also help explain the different rates of discharge. Looking picture of the battery stats showing uneven discharge it seems like one of the packs is supplying the load while the other is still sitting idle at 100% SOC. This is a common symptom when there is a OVP event since some BMSes (don't know these batteries, not sure if it applies here) will keep the battery at 100% SOC for as long as possible to help with cell balancing. The PACE BMS is one that does this.
It is likely that your charging voltage and float voltage is to high. Reduce it as already mentioned is the earlier post.

Also, did you read https://powerforum.co.za/topic/13599-dyness-a48100-solar-assistant-config/
Here the solution was to go to SA Beta.
A common mistake (i'm guilty as well) is to reset the battery every time you change the dip switches.

@JasonC ,
You may come right using the software mentioned in this post: https://powerforum.co.za/topic/12112-dyness-rs232-protocol-for-a48100/
In theory, you install this software on your PC, then use the SA cable plugged in the "COM" port of the master battery, configure the software according to what comm port the device manager has assigned when you plug the SA RS232 cable into the USB port.
Hopefully you can then monitor the batteries in real time.
If you keep the old one the Master, some info may be wrong/incomplete, as the slave with the newer F/W is probably sending more/additional info, that the Master does not know how to process/processes incorrectly, leading to incorrect data, but I'm just guessing here.
I did a lot of research on BMS's and the ability of getting info into other system like Home Assistant, and hence my choice of batteries. Getting real time data into HA was a breeze, but that was 2 years ago, and people have made integrations/add-on's etc. for all sorts of batteries and inverters these days. Hence my reason for moving from SA to HA.

PS, I only noticed now that your Solar Assistant cable is not plugged is to the master (or slave), so how does you SA setup get info from the batteries?
Maybe you just had the SA cable unplugged whilst taking photos.

Hi @JasonC ,
Disclaimer: I'm not a Mecer/Dyness fundi, so take my comments with a pinch on salt, but hopefully it may take you into a positive direction.
My Thoughts (and open too correction):
1) I read from the manual that the max charging voltage is 53.5V - that indicates to me that these Dyness Batteries are 15S, so your charging voltage is too high. You can see this that your highest cell voltage is 3.61V. Too close to the V cell max of 3.65V. These Voltronics (Mecer OEM) based Inverters are well known for there charging "overshoots".
2) The manual (only glanced through it), has a conflict in how to set up the dip switches. In the beginning of the manual, it states that (all) the slave battery must be 0000 (as your slave seem to be set at), yet where the parallel setup pictures are, it clearly shows 0010 for all the slaves.
3) Normal rule of adding newer batteries is as follows: a) Check firmware of old and new, and upgrade the old F/W to new. Haven't checked to see if there is F/W available on the net for these batteries. b) Make the newest battery the master. You can use the Solar Assistant battery cable plugged to your laptop to do this, once again, you will need the Dyness BMS monitoring software to do this.
4) the dip setting on the master = 0100, indicating you are talking to a "Axpert-king/VMIII/MAX, Growatt SPH/SPA(CAN comm), GMDE" via CAN @ 500k. Hopefully this is how your inverter is setup. There should be an indication on the LCD screen that the comms is OK. normally a "Li" symbol.
5) Before adding an additional battery, you need to ensure that the new and the old battery is at the same SOC level. Easiest to do that is by charging up the old, then disconnect it and replace it with the new one and charge it up to 100%, and then parallel them.
Hopefully other can add/suggest alternative things/methods, as I don't have your setup, so I'm just going on gut feel and old experience.
BR