Looks like it’s been fixed as new links once again work on timelines. At least on English Wikipedia.

In T428063#12007957, @Colinstu wrote:

Will anything need to be done manually on existing pages experiencing this issue? Or once the source code issue is resolved, suddenly all of broken ones will generate without an additional touch?

Either way, I'm making a note of these that are currently experiencing it:
https://en.wikipedia.org/wiki/Template:Timeline_of_Kindle_models
https://en.wikipedia.org/wiki/Template:Surface_timeline
https://en.wikipedia.org/wiki/Template:Timeline_Windows
https://en.wikipedia.org/wiki/Template:Timeline_of_Mac_operating_systems
https://en.wikipedia.org/wiki/Template:Timeline_of_Apple_Inc._products
https://en.wikipedia.org/wiki/Template:Timeline_of_iOS_and_derivative_operating_systems
https://en.wikipedia.org/wiki/Template:Timeline_of_iPad_models
https://en.wikipedia.org/wiki/Template:Complete_timeline_of_Mac_models
https://en.wikipedia.org/wiki/Template:Timeline_of_iOS_and_derivative_operating_systems
https://en.wikipedia.org/wiki/Template:Timeline_of_Mac_operating_systems
https://en.wikipedia.org/wiki/Template:Timeline_of_iPhone_models
https://en.wikipedia.org/wiki/Template:Timeline_of_Power_Macintosh,_Pro,_and_Studio_models
https://en.wikipedia.org/wiki/Template:Timeline_of_portable_Macintoshes
https://en.wikipedia.org/wiki/Template:Timeline_of_Mac_model_families
https://en.wikipedia.org/wiki/Template:Timeline_of_iMac_models
https://en.wikipedia.org/wiki/Template:Timeline_of_Macintosh_servers
https://en.wikipedia.org/wiki/Template:Timeline_of_compact_iPod_models
https://en.wikipedia.org/wiki/Template:Timeline_of_iOS_and_derivative_operating_systems

If manual touching is required I can go back later once there's an update here. Just didn't re-find these if they do require an effort.

In T428063#11987314, @TheEssay26 wrote:

So is it resolved? I've seen that it's been fixed.

In T428063#11986815, @GuardianOfArcadia wrote:

According to the diff and the HTML comment which was added by OreoStar-fait it seems to have something to do with wiki links.

I can confirm this as well: If I remove all links from the timelines mentioned above in deWP the timelines are working again.