I had the same problem while ago... check this out:
Upgrading broke everything (on Vanilla forums)
Not on NodeBB, for vanilla forums
I actually stopped by because I had the unfortunate experience of having my server shut down (it was being hosted for free at my friend's domain services company, and that came to an end), so I had to find a new place and restore everything from backups. I'm on DigitalOcean now but as you might remember, I am using Vanilla Forums, which frustratingly has many plugins abandoned by their developers. I took this opportunity to upgrade for security updates, etc. but then it broke some key features I was using, and TBH I'm not so keen on learning PHP to fix it.
Which brings me here: I'm actually waiting patiently for this one feature: automatically scrolling to the last read post, that is saved across devices. I know I harped on this a long time ago, but I forget if it was a UX or performance decision.
Having experienced this pain really motivates me to port everything to this platform.
I could be wrong, but I'm pretty sure that is something we don't save on localStorage, thus should work across all devices
EDIT: I think you should edit your title to include the software you're using
So do you want it to automatically scroll when you visit the topic, or after you click something else. Because there's a nice little alert that pops up when the topic is revisited that allows you to scroll back to your previous position.
That's the thing, I'm pretty sure that the popup you can click on is definitely something stored in local storage, I remember that that's how Baris implemented it, at least back then. Also, I can see that topics I've read are marked differently from topics I haven't read, but I'm still plopped right at the top of the thread.
The popup is an interesting idea, I can see where you'd like to see the topic beginning to get that context back, then scroll to see where the conversation left off; that's just not my use case, and I think @a_5mith and I are on the same page (see what I did there?) About not having to scroll through hundreds of posts to get where we left off.
This isn't really a complaint, more of a feature request, but mostly just an ask as to why the UX is the way it is. Is the vanilla forums platform the only one that does this?
If you want this that bad, I can make a quick plugin to do this. I don't think it would take very long.
I don't know whether the position is stored locally or remotely. However, either way, creating a plugin to do this and or implementing it in core and creating a pull request wouldn't be very difficult (I hope).
I know, it seems like all the parts are there, and it's been floating around in my mind to do it and make a PR but like I said it was more curiosity around why no one else would want that functionality in core...
Yeah, the bookmarking functionality is built using localStorage, although it's possible to move that out to a plugin so that it can handle both based on admin setting...
So I made a PR... I just wanted to see if this is something we can put into the core / concerns of doing so. Please give it a quick look to see if this is something that would be feasible: