How much have you been feeding?
How regularly?
Ph is very important. Even in soil.
Lots of the natives here in Australia repuire lower ph as a must. IMHO, certain bacteria thrive at different ph ranges. Its about letting the right ones thrive, that eat the right things, that in turn feed your plant.
If you have given a lot of NPK, id be cautious.
Whatever it is, your problems in the micro's. IMHO id be taking a stab at calcium or mag.
Did you supplement it with calcium, in the beginning? Either lime, gypsum, dolomite, calmag etc.
If you did, which is normal to do for soil. How much, and what did you use?
Whats the ph, at the bottom of your pot? Do you have any means of knowing ppm?
If you havn't fed in a LONG time, it may need a feed.
I think its pretty unlikely though.
Let us know the info, if you can, first.
Good luck.