To reproduce: Focus your crosshair on a block, then type in any of the following partial commands and attempt to tab complete the following coordinate arguments:

• /replaceitem block
• /spreadplayers
• /stats block
• /worldborder center

Since /tp has two ways to be formatted, it might not be desirable to add tab-completing for coordinates in this case, but for completeness' sake:

• /tp @p

will not allow tab-completing coordinates, likely because the destination player argument could follow just as well as coordinates.