Decoupling membrane yes/no?

[Navy]

Hello everyone, just a quick question hopefully.
I moved into a new build 24 years ago. Within 4 years I noticed a hairline crack on the kitchen floor tile roughly 18 inches long. Now, where the hairline crack stops I can see (with the sunlig0ht just in the right place) the adjacent tiles are also fractured but not cracked just a faint indentation in the tile. There is also another faint indentation at the other end of the kitchen. The kitchen area is 130cm x 250cm.
I'll add a couple pics to show the hairline crack.
Anyway, do I need a decoupling membrane or something else?
Any advice will be great.
Thanks

 

[Navy]

I plan to replace the tiles soon so trying to avoid a similar issue.

 

[aveatry]

The original concrete floor may not have been prepared properly. It can have sort of a thin scum on the top - can not remember what it is called. It dries and looks like concrete but is not attached, it needs to be removed before tiling otherwise it can cause problems like cracking.
That's my thoughts.
You only need decoupling on wooden floors as far as I know to separate the tiles from the moving wood