The mob spawner effects (the mob inside the spawner rotating & the flame particles) are not visible through glass. In my case, through blue stained glass. My friend have this issue too.
Thanks.
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MMK21
migrated
My friend is playing on Fancy/Fabulous and I'm at Fast graphics.
I think it's an ingame bug because of the new graphics engine Mojang uses.
galaxy_2alex
For better transparency support, use the "Fabulous" graphics mode - this is intentional, see MC-188529.
Which graphics preset are you using?