Iron bar top and bottom texture flashing when placed on top or under a block

when placing an iron bar(s) the texture of the top and bottom of it, (them), constantly flashes between it’s correct texture and the texture of whatever block it’s placed on and/or under.

can be replicated by placing an iron bar on top or under a block

video of issue: https://1drv.ms/v/s!AqXfUHUYXk0-djMXGoJ2qqY4ThQ