Ok i have seen that issue and i found a frozen lava stream only above one. most of these weirs shadows were random. Also, they sometimes vanish when i get close to them, and they always do when I fill a bucket with one of the dark lava blocks. Also, it doesnt only happen on lava. i will try to make a screenshot , but it's really hard. I saw it a couple times innether fortresses.
Alexis Tetar
Ok i have seen that issue and i found a frozen lava stream only above one. most of these weirs shadows were random. Also, they sometimes vanish when i get close to them, and they always do when I fill a bucket with one of the dark lava blocks. Also, it doesnt only happen on lava. i will try to make a screenshot , but it's really hard. I saw it a couple times innether fortresses.