if you want to know for sure the best would be to open a ticket with F5 support, they can actually look at the signatures and determine the exact cause.
as i said before the likely cause is that some dolphin browsers send a User-Agent header which doesn't match the list F5 uses. or some othe tool uses the doplhin User-Agent header wrongly.
the version you are using probably has a known User-Agent header and therefore isnt blocked.
to see if this is true is you can either capture traffic when you are browsing throught the ASM or turn on logging all requests (instead of only illegal ones) on the ASM and lookup your request. the different in your User-Agent header and the blocked on might provide a clue. but it still will be an assumption then, for an absolute answer log a ticket with F5 support (and please relay the answer here).