Normally, greatest problems with a major release of OS X, such as El Capitan, are in the earliest versions. As Apple then fixes those problems in successive updates, life becomes more stable and less fraught. There have been exceptions, when someone somewhere has decided to do radical things midstream, but they are unusual.

I am beginning to get the feeling that El Capitan 10.11.4 is – in some respects at least – one of those exceptions.

Take power management and sleep. In the last four weeks, despite being set to not put hard drives to sleep, the power cycles count on my Fusion Drive’s hard disk has risen by over 120. That means that the hard drive has been powered down, and back up again, an average of slightly more than four times each day. I don’t care what the Energy Saver pane might say, my iMac does what it damn well feels like.

Then the other night, just before I went to bed, I used the Sleep command to put the iMac to sleep. Just after I had finished undressing, I heard its startup chime, so went back downstairs to discover that it had suffered a “Sleep Wake Failure” and decide to restart itself. Although better than the freeze-restart troubles I had been having previously, it is another odd and worrying event. So for the moment I have turned off system sleep altogether, and the hard drive stays spinning steadily all the time.

But by far the strangest, and at the time most worrying of all, was last weekend. I keep a second admin user account, which is configured to meet the conventions required for screenshots for publication, including switching from the standard 5K display resolution down to 1280 x 720. I was just about to take the screenshots for the next Genius Tips section in MacFormat, went to change user, and all hell broke loose.

Normally the AMD Radeon R9 M395 graphics card in this iMac takes that in its stride. But this time, it went badly awry, as if it had had a couple too many beers. It tried to bring the Desktop up, but just couldn’t get each bit right. At first the (non-functional) menu bar looked good, but the rest of the Desktop was all over the place, and the Dock was nowhere to be seen. Then the menu bar got wiped out, and the Desktop was still in trouble. Eventually all went to a black screen and seemed to hang. I waited for the timed restart, but even that wouldn’t work, so forced a shutdown.

After a brief stopover in Recovery mode to check the Fusion Drive, which appeared fine, I got the iMac to start up normally in my regular admin account. When I manually enforced the various elements required for screenshots, including switching the display resolution, everything went fine again. But the logs reported no less than four kernel crashes to perform a “GPU Reset”. That doesn’t look good to me, and certainly got my palms starting to sweat.

So on this iMac, at least, 10.11.4 has been a succession of troubles, and I am hoping that 10.11.5 is not too far round the corner, fixing whatever 10.11.4 unfixed. It may even cut the thousand or so entries in the logs that seem to accumulate every hour that I am working – another indicator that several things are far from right.

From the many crash reports that my iMac has been sending Apple, they shouldn’t be short of clues as to what 10.11.4 has broken.