I have about 900 macros in 23 groups exported from KM8. I have an installer that imports those macros using importMacros applescript command. However, when imported to KM9, each macro gets imported in its own group, resulting in 900 groups.
It works fine in KM8.
Yikes. That's bad. I'm not sure if it's the way you saved the macros, but on a one-time basis it should be easy to fix because you can multi-select groups of macros (if they are consecutive) and drag them together into a different group. So at least that would get you going again, after which you can create correct new exports in KM9.
This is not something I have heard of. I suggest you send a few of the macros to support@stairways.com, together with details on how you import them and then I can take a look.
If you would like to share your AppleScript, maybe we can inspect and/or test to identify a cause.
Please put all scripts in a Forum Code Block.