Collections disappearing

[jimmyjobob41]

Losing collections within a collection set.  I created a collection set of grandkid photos, creating a collection for each grandkid.  When I close LR2, overnight the collections disappear.

Using the same process I used for the past several years.  Why do these collections disappear when I still have prior years collections?

[dj_paige]

LR2? That's 13 years old now. Is that a typo?

[GoldingD]

A few known issues in:

https://helpx.adobe.com/lightroom-classic/kb/known-issues.html