late last fall, dom sent me 4 cuttings for Persian White. i gave away one of them and kept 3. out of 3 only 1 survived. all died after rooting very well, and putting out great tops. two that died had very same problem as this one that survived. they were getting rotted on the new branch that was coming out. it seems either too much humidity in the humidity bin or too much humidity then sudden change in the humidity was causing the branch where there were lot of moisture to rot. 

this one was going down the same road and i didn't expect it to survive. however, the outside temp started to raise and once it hit low of 50, i moved it out to the partial sun and fresh air. it's still alive and now putting out a new leaves. 

i'm sure the "sick" area will be weak and i'll probably have to monitor it and possibly take air layer later this year or take cuttings to get healthier plant. 

this is one of the reason why i like to move my cuttings from stage to stage as quickly as possible. getting the cuttings to outside with sun and fresh air will prevent and take care of mold and rot issue on top. 

I hope it pulls through for you.  I don't use a humidity dome for this reason.

Boy I know how it is. I started out this year with very small plants.
Yes I know this is the hard way. Several lost there leaves, putting out new ones.
Most are looking better now that it is getting hot. It sure amazes me how hardy most of these figs are. Hang in there and keep up the good work.

South West TX
Zone 8