UPDATED MAY 27, 2023: Added an example with a chest generating in the same block as suspicious gravel.

Example 1 (three loot chests from the same ruin):

Seed: 443897344407718545

/execute in minecraft:overworld run tp @s -777 49 491 168 30

Example 2 (three loot chests from the same ruin; the top chest overlaps a suspicious gravel block)

Seed: 8139007336631598567

/execute in minecraft:overworld run tp @s 80968 38 69143

Normally, cold ocean ruins generate three times in the same location, one for each type of stone brick (regular bricks, mossy bricks, & cracked bricks). However, uneven terrain will sometimes cause the mossy brick and cracked brick versions to generate above the regular brick version, which can result in multiple loot chests. In addition, if the ruin generates on a chunk border, it may generate incorrectly in one chunk but perfectly fine in the other chunk. See attached screenshots.

As of the 1.20 snapshots, it is rarely possible for an offset cold ocean ruin to generate its loot chest in the same block where the non-offset ruin had generated a suspicious gravel block. The chest cannot be opened, and it drops itself without any loot if broken. If you start brushing another block, then move your cursor to the chest while still brushing, the chest is replaced by the suspicious gravel, but it doesn't drop any archaeology loot once brushing is complete (It's been reported that using a brush on the chest/suspicious gravel can cause a game crash, but I haven't been able to replicate this as of yet).