So, I opened a personal project file to work on a re-design. This file has been stable and easily worked-with for months now. It is a design evolution and is currently on version 3. So I opened it today, to see if I could solve some design issues that I have with the model, things that I do not like in the device being modeled. This file has been opened and worked on innumerable times, it has been fine. It's a background project which I work on when I have time. This time it did not look right, and when I took another look, it sure was NOT right. I found TWO huge and unacceptable issues which have a relation between them. I can see NO way in which "I" could be responsible for either of them. These are imported McMaster parts, which I have used for quite some time, and which have given no problems in the past. Now, they have, in simple terms, gone to hell in a handbasket. Issue #1: Two different bearings have somehow become connected, partially. The balls out of one of them have, at a totally different scale from what they were, become part of a roller thrust bearing. Issue #2 The other is the part from which the balls CAME (the one missing above is present in it still. It is at a MUCH bigger scale all of a sudden, it should have a 3/8" bore, but now measures out at 1". NO this has never been the wrong size before. Since ALL the parts that have so far been found to have errors now, were imported into Alibre and stored as ALibre parts, there should be no issues with "outside" parts. All imported files came in as STEP files. Correction: The two parts inside the ball bearing are "seals" from the original imported model of the bearing. But those parts remained the original size, at least they did not scale up with the other parts. No idea why. This sort of failure really needs an explanation of just HOW IT COULD HAPPEN AT ALL. The sub-assembly where the problem was discovered is part of a larger one, which is part of a still larger assembly. The top level has several subs, totaling up to quite a few parts and many constraints, etc when you consider all of them. It is a "big" assembly in the sense of being reasonably complex. It is not as big as many I have worked with. There MAY be OTHER problems that I have not yet found, which may not be limited to just this sub-assembly. The only conclusion I can come up with is that this mess is the result of the program allowing the available memory to "leak away", PLUS then NOT DETECTING the lack of memory, and so allowing the program to blunder ahead opening the file. There then presumably was a certain amount of over-writing of parts of the file. That may not be correct. At this point, the entire file is totally unreliable, and will have to be re-done in its entirety from scratch. Here is the (sectioned) sub-assembly where I spotted the problem. You can see that the ball bearings have become clearly outsized for the assembly.