We were beginning t upgrade from 9.1.5 to 9.1.8 on our test server. The admin had installed 9.1.8 and it was operational. We found out it was going to be significant work to get our custom panels and coding to work on 9.1.8 along with we were using ISIS and that was going to cause issues as well. Then we had some high-priority projects come in that we have to get done before we can devote all the necessary time to the upgrade. So the admin uninstalled 9.1.8 and then installed our current version of:
IBM Datacap 9.1.5 iFix01
Build: v 9.1.5.01098

Now I can't get claims batches to go through. We have DEV server also and it was never upgraded. The batches go through fine on there. The issue is that MC_Identify.dll is not creating the Autofld.dll object. See below snippet from the task log:

calling action SetMaxTolerantDistance (str="80") on P:TM000001
Loading RRX from DLL "d:\datacap\rrs\mc_identify.dll"
load rrx code: "d:\datacap\rrs\mc_identify.dll"
MC_Identify 9.0.0.19
Autofld.dll not created. Exiting.

On the DEV server it is successful and the log says this:

calling action SetMaxTolerantDistance (str="80") on P:TM000001
Loading RRX from DLL "d:\datacap\rrs\mc_identify.dll"
load rrx code: "d:\datacap\rrs\mc_identify.dll"
MC_Identify 9.0.0.19
Autofld.dll initialized
Autofld: dclogX enabled.

I have absolutely no idea how I can fix

You can try uninstalling and reinstall 9.15 again to see if that helps.  Maybe the mc_identify.dll is not registered.
Or download Depends.exe aka dependency walker and check if this dll is missing some dependency. 

Super long shoot.  Maybe the admin that install the software do not have rights to the comp.
https://www.ibm.com/docs/en/datacap/9.1.8?topic=SSZRWV_9.1.8/com.ibm.dc.reference.doc/dcaca950.htm
Try locating that user that install the software and grant the account rights.  See link above.