Hi @Sam8368
I've reported the issue (along with 2 others) and the technical team contacted me again this morning to say that they're still looking into it.
There are presently two ways of making notes. You can make a note directly on a booking (this doesn't help you if you want to make a note on an unbooked or blocked date), or you can turn on professional hosting tools and make a note on the multi-calendar (this doesn't help you on the mobile app).
Let's hope they fix it soon.