My Meyer lemon tree in a indoor container also has some flowers without a pollen tube. Also, some flowers have pale yellow (almost white) pollen on them instead of dark yellow.
It had put out a prolific bloom couple of months back but shed most of it leaves after that. Must have been winter leaf drop or some other stress. Anyway, it is sprouting new leaves now but is dropping all the bloom as the buds open up and mature and I haven't seen any signs of fruit.