I'm getting similar odd behavior on indenting and automated renumber of ordered lists. It is particularly noticeable at indent level 3. Rendered output is correct regardless of the raw text.
You can see that item "5" doesn't change.
Joplin 3.2.13 (prod, win32)
Client ID: 0b9eac1ab38b4d019ba53fed6546b685
Sync Version: 3
Profile Version: 47
Keychain Supported: Yes
Revision: a898e17
Backup: 1.4.2
Freehand Drawing: 2.14.0
Outline: 1.5.13