Over the last week or two, on both my Mac laptop and my iPad, sometimes when I am in the middle of a reply, the window goes blank and a box says something to the effect of another post was using this reply, and giving me the option of reloading the page. On clicking this I get my incomplete reply back but minus the last few lines I wrote.
Anyone else seeing this?
No problems here (Linux desktop using Firefox).
I haven't seen it recently but that problem is older than 2 weeks; as I never know of it's user error or forum software, I have not reported it.
I'm not sure if this happens in my situation with the Win10/Firefox or Android/Chrome; will try to keep an eye on it.
I see it occasionally on my Android tablet, never on my Mac.
I also experience this occasionally, definitely going back months.
I am using the forum from a Windows PC with Chrome browser.
Is this the one?
Yes, both on Mac 10.14.6 Mojave on Firefox. And iOS 15.4.1 (latest) with Safari.
Happened this morning and as I say occasional for the last few weeks.
Maybe some junk in your browser cache?
Happened to me at least once this week. Win 10.
I found an interesting related discussion:
I am able to reproduce it by following the instructions here:
(You can send yourself a private message via the forum system and then add replies to it to experiment because the Discourse forum software uses the same system for messages as for public topics)
That was claimed to have been fixed years ago, so maybe it was not completely fixed or there is a regression?
It is more understandable for it to occur under the conditions produced by those instructions, where you have the same topic open in multiple windows. I feel like I have encountered this message even when I only ever had the topic open in one window, but I never carefully paid attention to the specific conditions at the time so I might be wrong about that.
There was a recent report here:
This bug has been fixed a few days ago.
From the tag dates, it seems it was this one:
I guess the mentioned fix was one or both of these:
So this might mean that the previous occurrences of the issue I experienced were caused by a bug that was already fixed. You can determine which version of Discourse is currently in use by the Arduino forum by doing a "View page source" in the browser on any forum page:
<meta name="generator" content="Discourse 2.9.0.beta4 - https://github.com/discourse/discourse version c88ca23e8f657de747a5ad864978970f1bd3fa56">
So we definitely have those fixes in place.
That explains a lot about other wired stuff that kept happening with the unread list a few weeks back.
I never have more than one window open at a time, so it looks like it is not fully fixed.
What a brave new world we live in that holds such wonders.
I thought this new software was actually going to be an improvement, but it seems it is just a programmer's play thing.
From my perspective, as far as bugs and reliability go, there is no question that the Discourse-based forum we have now is a huge improvement over the old SMF-based Arduino forum. I think it is easy to forget how many outages and other problems the old forum had.
The bugs are rare and when they do occur there is an active team of developers working to fix them and maintainers to quickly update the Arduino forum to the new version. Compare that to the old forum where there was no hope of ever updating to a newer SMF version and only the most critical bugs were fixed, and even those fixes coming after a significant delay.
Although there were certain design/UX aspects of the SMF forum I preferred, there are also improvements provided by Discourse which likely offset the subjective downgrades for me.
Have you completed lost your mind?
Have you completely lost your memory? 
No it was never this bad with the old software, just the occasional outage. At least it looked the same on both portable and laptop systems.
The iPad experience with this new crap is horrendous.
The only plus it that replies don't time out any more in the middle of composition. The new forum categories are very badly worded almost as if the authors have English as a second or third language.
It works fine on my ancient iPad. Admittedly though, all it renders is a message telling me that my browser is too old and I will therefore get nothing, and like it 
Do you mean the category names? Would you mind sharing an example?
I looked at them and didn't spot any that looked bad. I don't think there have been too many. The ones I noticed which are either new or renamed:
Well, considering Arduino is based in Italy, most likely.
Both the category names and the general vocabulary use to label functions.
The worst offender is installation and troubleshooting, this would be better named IDE installation problems to stop people posting questions about there projects.
There is also the new Hardware section, this, if needed at all, should be called something like Arduino boards or Arduino variants. You get a lot of posts under this that are just general posts. Then beginners tutorials section is too complex a concept for some beginners to comprehend it is for posting tutorials not for asking their own questions.
In all there are too many categories, and it is difficult to choose the right category.
Also the words choice for indicating actions are poor. The worst offender in my book is the use of "defer" I know one of the meanings of the word is to put off some action, and in this case the action is marking the post as unread, but in English English, it's main meaning is to give way to another. Why not just use "unread"? Also why is this an option you have to enable?
That and more, like the way all the HTML macros disappear from replies on an iPad. We were promised that one of the major reasons for moving was so they could support mobile devices better, well a big fail on that one.
I wouldn't go so far as making the category specific to installation of the IDE, but certainly the category name is ambiguous.
However, surely this category could only be considered "new" on a geologic time scale?
I agree 100%
It does seem cryptic.
Thinking about it now, I have never used that feature and I'm wondering if it is because I instinctively ignore this mysterious button.
It is somewhat inconsistent with the other action buttons in that it is not a verb. Probably an improvement over "defer" even so. I don't have a better suggestion.
Do you mean HTML tags (e.g., <b>)?
Yes.
It is possible that you have never seen it because by default it is disabled in your settings. It took me some time to find it.
Well many people, mainly first posters, fall into the trap of posting here every day.