There was a bug in the code that prevented to finding of a portal location if the player entered from the side.
It can happen only if the portal frame is removed, but as in vanilla it is possible, then it needs to be addressed.
The fix itself is simple: instead of checking just up from the starting location, the code will check all blocks in 10x10x10 square from the starting location and find the "closest" portal location.
This will fix#2237
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