Blocks that connect such as chests, fences, iron bars, etc. don't connect to other blocks that they're suppose to (or of the same block). I have provided an example picture. Please note that updating the block only works until they are updated again. You cannot walk between them (example: between two glass panes), but can still interact with blocks behind them (example: hitting a dragon egg between glass panes).
Note: This only happens on servers that support multiple versions, but I don't know for sure because I can't find any 1.13 only servers.
Note 2: They work normally on realms