I saw a similar topic created about hlines. So, it would be rather a feature request to add hlines rather than bug. Here is fragment of conversation I am talking about for reference:

 I start with 



 | Example | Text    | Dates        | other   |
 |---------+---------+--------------+---------|
 | this    | comment | <2022-01-28 vie> | nothing |


 That is converted to 



 +---------+---------+--------------+---------+
 | Example | Text    | Dates        | other   |
 +---------+---------+--------------+---------+
 | this    | comment | <2022-01-28 vie> | nothing |
 +---------+---------+--------------+---------+


 And is converted back to 


 | Example | Text    | Dates        | other   |
 | this    | comment | <2022-01-28 vie> | nothing |


 Couldn't in the last step the hlines be respected?
That would not make sense.
AFAIK, table.el has no notion of hlines. The +---+ separators in
table.el tables mark cell boundaries, not hlines.