IC manufacturers are not always innocent when it comes to strange things happening when using supposedly identical devices only separated by a fair few years between manufacture.
I had to work on a piece of equipment which used a mono stable IC in the 4000 series, where it was used to provide a quite long "on" time.
Unfortunately, one of these devices became lost.
"No worries, there are plenty in the Store!"
When I tried to use the new one, it kept timing out early, so the equipment didn't work.
The same result with all the new ones in the Store.
It turns out that the manufacturer originally specified the mono for a very large range of "on" times, but some users had problems with them with short
"on" times.
The answer was to change the design, so that the original part number was good for fairly short durations, & introduce a new part number for people who want long durations.
We had to specially order the "long duration" version, replace the originals with the new type in both the units using them, generate an internal Tech note, & change the original schematic.......Aaaarrrrgggghhhh!