I see a change of file wodFtpDLX.dll between UE v21.10.0.xxxx (DLL has version 22.214.171.1242) and UE v126.96.36.1994 (DLL has version 188.8.131.522). Most likely the problem is caused by a bug in new version of this FTP client DLL.
Please report this issue to IDM support by email.
Most likely it would be best to pack with ZIP or RAR a copy of %APPDATA%\IDMComp\UltraEdit\uedit32.ini which is copied after using button Clear history at Advanced - Configuration - Toolbars / Menus - Miscellaneous and UltraEdit is closed. Also added to the ZIP archive should be the file containing the FTP account data which is by default also uedit32.ini as long as having not specified a different file at Advanced - Configuration - FTP.
The email should contain detailed instructions for reproducing the problem. As the IDM developers need to access your server, you need to explain in the email which data the IDM developers can access to look what is the problem. So it would be best to create a data file just for this testing purpose. If it is possible for you, you could create a user account for the IDM developers to access only this data file and nothing else on your server. The FTP account dialog should in this case contain only the data for this special test account before copying uedit32.ini respectively the FTP account data file, packing it with ZIP or RAR and attach the archive file to the email.
Very important: Explain in the email that upload is not working in UE v184.108.40.2064, but works in UE v220.127.116.111 with same account settings and with same UltraEdit configuration, most likely caused by updated wodFtpDLX.dll.
Bugs in code can be fixed only if users report them and the problem is reproducible. That is the reason why I suggest to report this issue to IDM support although in this case it is not easy for you to prepare the data needed for reproducing the problem and you need to grant IDM access to your server as I'm quite sure that IDM has not any or even better same z/OS system running to verify the problem by themselves.
PS: If you are using a personal firewall on your computer, you have hopefully configured that not only UE v18.104.22.1681, but also UE v22.214.171.1244 can pass it.