For multiblocks where full blocks turn into partial blocks, when they form, adjacent blocks remain transparent.

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Here's an example from single player. Create a tank and surround the top row with stone blocks.

• Minecraft 1.17.1
• Forge 37.0.59
• Immersive Engineering 1.17.1-5.0.2-pre.119
• Journeymap 5.7.3rc3
• Just Enough Items 8.0.0.14

just got this and I'm confused, but it may help reproducing
done in superflat
the generators' orientation lengthwise is east to west, the generators with transparency are having their Generator Blocks facing east

note that mirroring the Diesel Generator did not affect transparency in this instance

I'm unable to reproduce this. Have you tried in a singleplayer world? Do you have any additional mods installed (compared to what's in the gist)?

I can reproduce this, but only at one section of my base: this metal press up against this wall. (Also on the 1.17 test server)

Only extra mod I have from the gist is "journeymap-1.17.1-5.7.3rc3". haven't tried to replicate in a singleplaye world, but will give it a crack when I have some spare time.