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The end portal spawns on the north side of the end portal. And the only way for it to spawn, is to place the last placed ender eyes on the northern part of the portal. the northern side of the end portals, are also faced, "west", from looking at targeted block in F3 mode. Normal end portals in strongholds work fine.
Environment
PC Specs:
AMD Ryzen 3 1200 3.1 GHz Quad-Core Processor
ASRock AB350M Micro ATX AM4 Motherboard
Gigabyte GeForce GT 1030 2 GB Video Card
Operating System:
Windows 10 Pro
Java Version:
Version 8, Update 231, build 1.8.0_231-b11
Duplicate of MC-97216. If the end portal blocks are not placed in the proper orientation, the portal itself may generate as you have presented.