Mac Mojave Sys Prefs/Screensaver slows down, locks up

iMac (2019), 10.14.6 - I had the same issue. I knew that the problem was Mojave Security Update 2020-004, because a bootable backup made before the update did not show the problem. After much troubleshooting, I reinstalled the operating system by booting up using Command-R. That reinstalled 10.14.4, which I then updated to 10.14.6. The reinstalled OS did not include Security Update 2020-004, and the screensaver now functions normally.

Yes! It is now fixed.

I found downgrading to original Mojave wasn't viable. I forgot that over the past year or two updates have made irreversible changes to our firmware, such that the updated firmware conflicts with older macOS versions. My Mac was creating firmware .dumb files!

Now all updates available applied as of 12/24 and the problem is fixed. I think fix was in Security Update 2020-007 Mojave https://support.apple.com/en-us/HT212011, released 12/14/20.

FWIW, the security update broke all photo-based screen savers. The workaround for now is to select any non-photo screen savers, Flurry, Shell, Message, etc.

+1 to Alfi, the latest Mojave Safari/Security update has fixed the issue for me, as well. Happy holidays, gang.

Today an update(Security and Safari appeared.

I did it AND BUG IS GONE! Fotobased Screensavers load without noticeable delay and no freezing

!! 1000 Smileys!

this last security updates fixed the problem.

it still works on two computers (Macbook pro and Imac)

So it should also work for u. (i didnt make a reinstall:

I had the same issue. When I updated to Big Sur issue resolved.

TY for ur Information! Please report here:

https://www.apple.com/feedback/macos.html

as Allan Jones recommends.

May an update by Apple follow soon.

Hi, I had exactly the same issues it’s all started after Mojave Security Update 2020-004 & it affects screen savers with photos in them.

My solution for now is to use the Message/Text screen saver for now my device won’t keep freezing but it’s annoying that an update missed up an Apple system screen savers.

After the last update today has the problem gone away for anybody here?

For me NO, still the Computer becomes unresponsible for 10 too 30 seconds and more

Especially when u just load the photobased screensavers in preferences A process like Ilife showing about 30% CPU usage

Sorry yes , i was distracted after posting, now editing of my fault is not possible.

No improvement.. still my mac becomes unresponsive for up to a minute.

i have this on 2 Macs (my imac and my wife`s Macbook pro.)

From software revision "Big Sur" the screen is filled with an ugly bright RED and Orange screen......at least with Catalina it was a picture of the island -- here we get pop-art .

I have set one machine to just go to black screen, but I would like to randomly show travel pictures --

I'm having the same issue here on my Mid 2012 Mac Pro running 10.14.6 -- submitted my bug report today. Hopefully we'll get a fix soon.

No change here. Super frustrating.

Sorry but the problem comes from security update 2020-004 (July 2020) so its not to be exspected that this update aims at this bug.