I had a few issues lately while trying to load CD-Rs of my community compilation. They just wouldn't load, the disc would spin very slowly but it would never leave the boot animation. And it wouldn't load discs that had worked in the past either. I had assumed at first that the drive had stopped working entirely but found that my official disc of Guardian worked just fine, and booted very quickly in fact.
So, the first thing I tried was purchasing a CD lens cleaner kit. This was the specific one I purchased but I'm pretty sure any similar kit would be just fine.
Curiously, although the cleaner disk features instructions on audio tracks, they wouldn't play at first. The CD drive would whirr to life for a few seconds, and then die out and stop completely. But after I removed the disc and re-inserted it, the audio started to play. It skipped a fair bit at first so it was difficult to listen to the instructions, but after repeated attempts the audio became clear. So at least the lens cleaner objectively made some improvement.
My old CD-R games begun to work again, perhaps loading faster than they ever had in the past. But unfortunately, my new CD-Rs didn't work. I tried burning to multiple discs, with no success. I figured that the problem now was the brand - my old CD-Rs were Verbatim printable discs, my new ones were branded with the generic brand of a stationary chain. A new spindle of Verbatim discs worked just fine.
So in short, if you can't get CD-R games to work on a CD32:
1. Clean your lens
2. Use top quality media. Even if your generic CD-Rs work just fine in a high quality, modern CD drive, the CD32's drive is lower quality so use top quality discs to compensate.