I have seen a similar thread on this issue, but it is two years old, and my problem seems to relate to new firmware.
I have a Kobo Aura HD. It has always been a bit balky in its highlighting/ note-taking functions.
(I beg Kobo: make these functions better in the next generation!! They are the key to your device being really useful to serious readers--you already have great visual quality, fonts, adjustments, etc.)
After firmware upgrade 3.15, this syndrome developed:
If I open a book, the first three highlights or so work as well as the function ever did (i. e., slow, but functional). Then subsequent highlights are slower--it is as though a cache is filling up (?). Then, after about the fifth highlight in a particular book, a touch that is meant to highlight : : turns a page. Then, if I go back to the page, I can highlight, and the cycle resumes: I get one-to-three "free" highlights, then balkiness, then page-turns in response to highlighting attempts.
I called Kobo and they recommended, and I performed a hard factory reset (the one that wipes all contents from the machine--so I had to reload the books, etc.). This reset had no effect on the highlighting problem at all.
Does anyone else experience this? Anyone know of a solution?
Thanks.