After quite some time I returned to my private wiki and found out that the footer lines were not working anymore. They were all formatted as an one liner:
[[./sidebar?do=edit|✔]] · [[./:|<]] · [[../:|<<]] · [[../../:|<<<]]
and worked perfectly for years. Now they appear as:
✔ · [[./:|<]] · [[../:|«]] · [[../../:|«<]]
Only the first link is active, all other are rendered as pure text. Reformatting to:
restores the old and expected behavior with active links:
✔ · < · << · <<<
So any text BEFORE a link (internal and external) does something unexpected. The problem is not a general one because I found another installation with the same version and plugins which does not show this behavior. Any advice or hint is highly appreciated as I do not have any idea what might have caused this.