Couple of things:
>>I've been getting random errors using Driver Type thin.. so I wanted to try OCI
Like, what exactly?
That's not a good release to be using. The terminal version of 3 was 3.0.12 (as in twelve)..and even that is very old. Better to get a copy of version 19.1/19.2 and try that with a THIN connection before proceeding with anything else.
users get random 500 internal server errors..
logs show ORA-01460: unimplemented or unreasonable conversion requested
but at random times, sometimes even just after they click Logon
if they refresh their page, F5, then they can continue working
I am using 3.0.2 because when I tried a newer version it did not function behind our load balancer, some security change in 3.0.3 and higher..
I am planning on trying version 19 though as soon as I get a chance to see if it works..
>>logs show ORA-01460: unimplemented or unreasonable conversion requested
I usually see those when someone is using our stuff on an older database, like 9i or 10g
the databases are 220.127.116.11
apex is 5.1
weblogic hosting ORDS is 18.104.22.168
pretty sure the java/JDBC it is using is ojdbc8.jar
after you upgrade, if you see the error again, there should be some SQL/PLSQL attached to it - we'll need to see that to determine what's happening
Your APEX is also pretty old.