The bug

All map decoration sprites are 8x8 images. This is an issue since some of them have odd centers (line of symmetry is through the center of a pixel, rather than on the border between pixels), which can cause them to appear slightly misaligned on maps in practice.

Bedrock Edition gets around this issue by resizing map icons to 16x16, and shifting the affected icons by a pixel such that the line of symmetry correctly bisects the sprites in question.

It seems as though this resizing happened in preview version 1.20.40, making this a recent enough change to constitute a parity report.

How to fix

Resize the map icons to 16x16, and for the affected icons (player, frame, red_marker, blue_marker, target_point, target_x, trial_chamber), move the sprite by one pixel on one or both axes so that the image becomes properly aligned.

I've attached a resource pack that fixes this issue for all of Java Edition's map icons by resizing and translating accordingly. I've also included Bedrock Edition's seven exclusive icons as to fix MC-269713, as well as the two sprites which should be added to Programmer Art as to fix MC-265265, which are sized and positioned as is correct.