Why can I NOT use PNC Mobile app with Samsung S-3 Android version 4.4.2?

I can download app from Google Play Store but will not let me log in. Error message: "Unfortunately, PNC has stopped". I have used this app for years without problem. I have uninstalled app, restarted my phone, then downloaded app and reinstalled with the same result. Problem began with latest app update. PNC indicates that my phone is too old and not compatible with latest security requirements. Does this sound reasonable? Very disappointing.

It sounds very reasonable. They've updated the app in a major way about twice in the past few years. The problem I have is that there hasn't been an update since I got my new phone, and the old one was running 4.4.2, and the app still worked. I know it was working, because a few deposits went in - and I made them with the phone. (But that was on a Note 3, and it had a lot more than an S3. It's possible that the new update just won't run in a 1GB space.)

I'd try clearing the app cache (in Settings/Storage), then starting in recovery (Volume Down/Home/Power) and clearing the system cache - don't clear the system data - then restarting the phone, installing the app (I assume that you've uninstalled it already - if not, uninstall it before starting any of this) and see if it works. If not, you're in the position I was before I bought my Note 3 - buy a newer phone or don't use your phone for the bank. (You can still pay your bills and check your balance on a PC, or even on a web page on the phone, but you'll have to go in to deposit checks.) But remember, the S3 is going on 6 years old. There are a lot of things that won't work in it - probably Walmart Pay, definitely Samsung Pay or Google Pay, etc. (And any app that needs more than 1GB of RAM - and we'll be seeing more and more of them as the "smaller" phones come out with 2 or 3 GB of RAM. It's usually due to sloppy programming, but it happens.)

I really doubt that the problem is the security requirements - I'm not even asked for my unlock code when I run the app - let alone a fingerprint. (But the customer service department of PNC isn't filled with software developers, all they know is what they're told to say.)