No I do not think it is drought stress or a pH problem. I think it is a disease but not one I am familiar with. Leaf lesion could be the same thing that is killing the stems.
Where are you located?
The leaf spotting looks a lot like drought but I never see the shoot die back in drought situations. I attach a picture of drought symptoms where leaves are burned.
You can go like at some disease images here.
Shoot dieback could be anthracnose or phomopsis. We we culture disease organisms out of collapsed shoots like this we get lots of things indicating they came after the shoot tip died.