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B3NN3TT · Nov 10, 2015, 03:26 PM

Having a strange problem that I don't know how to begin searching for.

Core i7 Macbook Pro (Sandy Bridge), running El Capitan. The problem doesn't happen often, but every once in a while it will show itself, and ruin my day.

There are two user accounts on the machine - one for me and one for my wife. So we switch back and forth a lot. From time to time, seemingly completely randomly, I'll find myself stuck on the user switching screen, and it's completely unresponsive.

I choose my user name from the top right menu, and the user switching/login screen comes up, with the field to enter my password. But when I click in the field, there is no response, no cursor. There is a "Cancel" button at the bottom of the screen, but clicking THAT gets no response either. So I can't type, can't click; I'm stuck on the login screen with no option to back out and none to move forward.

Stranger still, if I hit CMD-TAB while stuck on this unresponsive screen, I can see the apps switching on the desktop behind the login window's gray background. So my input is apparently being applied to whatever app is in the foreground of my wife's user account, and not to the user-switching interface.

I let it sit for several minutes in this state, thinking it might "wake up" eventually, but it never does. I have no choice but to force a shutdown by holding down the Power button.

Again, it seems to happen at total random intervals - at least I've not been able to ascertain any pattern to when and why it happens.

For the record, I can't be certain, but I'm pretty sure this was also happening back in Yosemite, and El Capitan has not changed anything.

Any thoughts as to what might be causing this, or where to start looking?

ibook_steve · Nov 10, 2015, 06:23 PM

Does it only happen when you're switching FROM your account TO your wife's account? She might have some login item that is causing the problem. Check those out in the account settings. Also try creating a dummy account and see if you can reproduce the problem switching to and from that account.

Steve

B3NN3TT · Nov 10, 2015, 08:12 PM

As far as I've observed, it only happens when switching from HER user account to MINE. She's never mentioned seeing anything unusual when she switches over from mine to hers. This only happens when both accounts are already logged in, and just switching from one to the other. We never log out; we just switch back and forth usually at least 5 times a day, with no problems, but every so often I get the "freeze" (which isn't really a freeze in the truest sense of the word, but you get my gist).

reader50 · Nov 11, 2015, 12:03 AM

Second ibook_steve's suggestion. Create another account, and narrow down if the problem is:

A) Leaving her account
- or -
B) Entering your account

The intermittent nature of the problem will be annoying to work around. Try always switching through the test account, until the problem has happened a few times. Her -> test -> You. You -> test -> Her. Enough times you're sure where it sticks. My money would be on A).

You could pull up the Console log right after a reboot. Scroll back to see if anything interesting was listed. You could also run hardware diagnostics. A single bit of bad RAM can cause intermittent issues.

B3NN3TT · Nov 11, 2015, 10:32 AM

Good; thanks for the suggestions. Agreed, an intermediate account with no "baggage" might reveal something.

And yes, the issue seems to be with leaving her account; it's like the system doesn't want to let go of whatever's happening over there.

I think I have a RAM diagnostic app around here somewhere... will have to check for that when I get home today.

If anyone else has input, fire away - and if I have any new developments to report, I'll be back! Thanks.

P · Nov 11, 2015, 11:44 AM

The obvious hint is to check Console.app to see if there are some smoking guns in the log files. Also check for autostarting applications in System Preferences and old drivers for things like mice.

B3NN3TT · Mar 2, 2016, 08:51 PM

Back with more details on this issue!

As expected, the problem has reoccurred several times since this discussion, and sometimes when switching from my account to the wife's, and even the new clean user account. But it finally caught me at a moment that I had a chance to check the console, and found an INORDINATE amount of entries from a Wacom tablet driver at the time of the "freeze".

I have now deleted the Wacom software entirely, so I'll give it a while and see if that changes anything.

Sadly, it's such an intermittent and unpredictable phenomenon, I never know when or how often it will occur. But if there are any more noteworthy developments, I'll update here, in the interest of thoroughness.

ghporter · Mar 2, 2016, 10:13 PM

I'll bet deleting the tablet itself AND the software completely eliminates the problem. It sounds like those "freezes" were due to the tablet and its software screwing up. It may be a hardware thing, maybe a software thing. The only way to tell is to reintroduce the hardware (by itself) for a while, and then add a fresh install of the software.