This bug still occurs in release version 1.20.4.
I found at least three incidents within 5 minutes of flying around the first world I created to confirm it. It is not 'substantially rare'. I would also note that it does not occur only at chunk borders (see screenshots).
Seed: -7722129573582750484
Affected locations: XYZ(410,69,-1337), XYZ(400,70,-1310), XYZ(503,70,-1206).
Ironically it seems this issue was originally a quirk of the Java edition, as it apparently did not occur in Bedrock, until the bug was introduced in Bedrock (and mislabeled as a 'resolution'), see MC-240106.
I did some more testing to demonstrate how common this bug really is.
Here's the seed from MC-240106: -1127564142
Once again, within a few minutes of flying around, I found the bug at several locations:
XYZ(254,75,-216), XYZ(243,61,-228), XYZ(284,61,-248),
XYZ(251,60,-295), XYZ(612,71,-429), XYZ(1073,74,-674),
XYZ(1098,71,-693), XYZ(476,73,-1082), XYZ(479,70,-1041)
Note that the incorrect transitions are most apparent when the aquifer is situated above or next to a cave. In the worst cases, the aquifer hangs over the cave like a bowl. The correct behavior (apparently seen in Bedrock beta 1.18.0.24) is to have the entire crater or cave filled with water if it borders or intersects an aquifer.