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iMac suddenly lagging for short periods of time, but very frequently. How can I diagnose the issue?

techno_telemann

techno_telemann

macrumors newbie
Original poster
Aug 12, 2019
3
0
2019 iMac 5K on 10.15.7. This started within the last week. I notice it primarily when my cursor starts to lag around the screen. Can't be an issue with the mouse because it happens with my trackpad as well (these are the official Magic Mouse/Trackpad). I've tried watching the Activity Monitor to see if anything is spiking when the lag occurs but nothing seems unusual. Also called Apple Support, and they had me reset the SMC and restart in diagnostic mode with no results. Any ideas?
 
I get the same on my 2017 27" iMac and I think it started happening after the Safari 14 update. I'm also using a magic keyboard (with keypad) and trackpad. It's intermittent and happens a few times a day.
 
I've had problems in the past with certain USB devices interfering with my mouse. I think it was an external SSD. What if anything do you have on your USB ports?
 
Feek said:
Nothing has changed here, nothing whatsoever. I'm pretty sure it's not RF related.
Click to expand...
There's only one way you can be sure of that, and that is to wire in and see if it keeps happening.
 
rkuo said:
There's only one way you can be sure of that, and that is to wire in and see if it keeps happening.
Click to expand...
My iMac is connected via ethernet, it's not connected to the network via WiFi. I'm a radio ham, there's often very high RF fields in my shack/office and it's totally unrelated to when I'm transmitting. Trust me, it's nothing to do with RF. I have a USB mouse connected for one particular ham radio application and when it happens, it's the same with the trackpad and the mouse.
SmallDane said:
Perhaps. But try unplugging USB devices and see if it makes a difference.
Click to expand...
It's not USB. It's definitely linked to Safari. It happens most when I open a new tab and it's loading a web page.
 
Feek said:
I get the same on my 2017 27" iMac and I think it started happening after the Safari 14 update. I'm also using a magic keyboard (with keypad) and trackpad. It's intermittent and happens a few times a day.
Click to expand...

Could this be the cause if I hardly ever use Safari? I primarily use Firefox but I experience the lag no matter which programs I have open.

SmallDane said:
I've had problems in the past with certain USB devices interfering with my mouse. I think it was an external SSD. What if anything do you have on your USB ports?
Click to expand...

Currently, I have an external SSD, audio interface, thumb drive, Apple SuperDrive, a wireless charger, and an external webcam plugged in. These were all plugged in and working fine for (at least) weeks before I started experiencing problems.

As an added note, it is definitely more than the mouse and trackpad that are affected. It seems like the whole system slows down for 10-15 seconds at a time, and I can sometimes notice it when the input from my keyboard slows down.
 
techno_telemann said:
As an added note, it is definitely more than the mouse and trackpad that are affected. It seems like the whole system slows down for 10-15 seconds at a time, and I can sometimes notice it when the input from my keyboard slows down.
Click to expand...
Agreed, the entire system goes on a slowdown, it's not just the mouse being jerky.

techno_telemann said:
Could this be the cause if I hardly ever use Safari? I primarily use Firefox but I experience the lag no matter which programs I have open.
Click to expand...
Good point - It only seems to start for me when I open a new tab in Safari though and it's not every time.
 
Try removing spotlight indexing from your external drives. Check what is in your library/launch daemons and launch agents folders, as well as system preferences/users/login items.
 
Feek said:
I get the same on my 2017 27" iMac and I think it started happening after the Safari 14 update. I'm also using a magic keyboard (with keypad) and trackpad. It's intermittent and happens a few times a day.
Click to expand...
Quoting myself.
This did fix itself some time after but it's started again with the Safari 15 update. Exactly the same as it was when I first updated to Safari 14.
 
temporarily move everything out of launch daemons and launch agents folders under library, and also check system preferences user logon items. Also while your at it unplug any usb stuff other than mouse and keyboard. Restart a couple times and see if it still happens, then feed stuff back in slowly.
 
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