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

[techno_telemann]

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?

 

[Feek]

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.

 

[rkuo]

sounds like wireless interference.

 

[SmallDane]

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]

sounds like wireless interference.

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?

Nothing has changed here, nothing whatsoever. I'm pretty sure it's not RF related.

 

[rkuo]

Nothing has changed here, nothing whatsoever. I'm pretty sure it's not RF related.

There's only one way you can be sure of that, and that is to wire in and see if it keeps happening.

 

[SmallDane]

Nothing has changed here, nothing whatsoever. I'm pretty sure it's not RF related.

Perhaps. But try unplugging USB devices and see if it makes a difference.

 

[Feek]

There's only one way you can be sure of that, and that is to wire in and see if it keeps happening.

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.

Perhaps. But try unplugging USB devices and see if it makes a difference.

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.

 

[techno_telemann]

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.

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.

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?

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.

 

[Feek]

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.

Agreed, the entire system goes on a slowdown, it's not just the mouse being jerky.

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.

Good point - It only seems to start for me when I open a new tab in Safari though and it's not every time.

 

[xgman]

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.

 

[ssmed]

Mojave and Safari 14 bug ? The update was pulled.

 

[Feek]

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.

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.

 

[xgman]

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.