It seems that blocks that use a condition to check if they should naturally generate or not sometimes ignore the condition.
While modding for 1.12.2 I had some Nether plants with a "on block added" procedure that removed the plant if the block below was air or another plant.
In 1.14.4 "on block added" trigger does no longer work on natural block generation so I had to create a condition instead. However, the plants still spawn in the air, ignoring the condition.
I will soon provide some screenshots about the plants and the procedure