I've had a similar weird timing chain experience on our triple this week. Just got back from a trip to Europe where we took our coupled triplet. Timing chains were tight when I disassembled for packing (I pulled the cranks for packing). I put it back together this weekend, and the rear-most timing chain is now noticeably slack. First, I swapped the two timing chains (which have the same amount of links and are same vintage/brand). Same deal. Then I thought the eccentric(s) must have moved somehow. But, I put an alignment mark on the eccentric and frame (using a Sharpie) before we first packed the bike, and they are still perfectly aligned.

It's easy enough to fix, I'll just adjust the eccentrics. But the *why/how* it happened escapes me. Any thoughts?