One thing that happens more often than in the past is the gold plated fingers on the edge of the PCB flake off when you remove them. It's an unintended consequence of the RoHS ban on lead based solder. The gold is just an electroplating on top of solder on those fingers. When lead based solder was used, the exposed edges of the lead formed lead oxide that acted as a corrosion barrier. When RoHS removed the lead, the lead oxide barrier is gone now too and the solder used in its place corrodes over time. When you pull the card out, the gold flakes off and/or stays behind in the socket, so when you plug an old board into a new socket, it doesn't make good contact, or if you plug a new board into an old socket, the old gold is jammed in the pins and shorts them. This issue exists with all electronics but is especially prevalent in things that have plug in boards, plus things that are exposed to contaminants. VFDs fall into both categories because of all the option boards people want combined with the high volume of cooling air flow they need.