Nothing has changed in this part of Opus for a while, and since it's also intermittently working in Explorer, I'd say the problem is either in the phone or on the PC as a whole.
A Windows or iOS update may have changed the MTP stack on either side, or antivirus may have changed and be treating things differently, for example.
MTP in Windows, Android and iOS is not that reliable at the best of times, so rebooting the phone and PC may also help in case something is stuck.
Some of the suggestions here may also be worth a try, for those that apply to iOS as well: