Cannot recognize the Battery cell to be changed

sorry to hear about your issues; but on a 15 year pack that bakes in the AZ sun - replacing 1 in 28 batteries is like playing wack-a-mole.

The way the batteries are chained together, the Dr. Prius app is giving you a location on where it thinks the dead cell is. You still need to do an individual cell voltage and load test. A simple voltage test isn't going to cut it, since your can have voltage, but the battery's load output could be very low or zero. As most people know, a battery's load output of zero is useless. It can't perform any work; that's why you need to separate it out of the network to test it. Trying to test for a bad cell within the network, the bad cell can rely on adjacent cells to pass the test.
According to your jpg; you've got a minimum of 6 questionable cells, 3 pairs that need testing. You should test all of them, when you have the pack apart - otherwise you'll be doing this again in 6 months or less. Look up: load testing a battery and why. YouTube and google are a great resource and learning tool; but the devil is in the details. While most YouTubers don't profess to be experts; there is good information mixed along with very bad information that can be outright wrong and dangerous. Just like here.....

Good Luck...

 

Monitoring the pack in real time is the key to locating weak modules. The two pics below show a full throttle acceleration from a dead stop, (146 amp draw) and a milder 31 amp load, while backing up an incline. In both cases module #27 was weak. Repeated cycling of #27 right in the car did not bring it back to life, so the pack was removed from the car, and #27 was replaced.

 

So you mentioned getting the RTOD. If it is the HV battery, you likely have a P0A80 and perhaps an additional code P30xx to tell you which block. If only a P0A80, then the car knows there's an issue, but hasn't determined exactly which block yet, but it will.

The P0A80 will allow you to continue driving normally. Once the P30xx triggers, the car will essentially go to limp mode.

 

You're in the early stage where "voltage diff." is still relatively normal most of the time so keep grabbing screenshots of Dr. Prius app as you clear the triangle during the still rare abnormal time. Then when you have time to pull the pack load test everything and then review all your screenshots to decide on which modules you wanna replace.

 

In the early stages of deterioration a charge and balance and a few rounds of reconditioning can make a huge difference of bringing a pack back to normal, but if you're constantly pulling more than 1.0 volt in voltage difference that's a bad cell that's not gonna get better and that module needs to be replaced.

 

The loss in power is usually the engine computers sensing a problem then throwing a red triangle and then going into limp mode where you only have engine power not electrical power.

Did you inspect the voltage sensor plug where it plugs into hybrid battery ECU? That connection tends to corrode and fry that ECU. Also it's possible person you bought modules from sold you some bad ones.