Frogs often get stuck beneath lilypads.
[media]To reproduce
Spawn some frogs near a one block high water pond with lily pads. Eventually they will get stuck there.
Alternatively just place a lilypad and spawn a frog with a spawn egg underneath.
Video
[media]22w19a:
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I can concur that I see the same issue. If I break the block in front of the frog, the frog starts moving around like normal.
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