I faced the similar bug a couple of times and I thought it's due to the internet outage while posting but when I checked the post history, it's not actually there so I have to close the tab and cause even refreshing gives the same bug.
Probably this bug is due to the increase of traffic in the forum?
While it is true that the forum's traffic has increased, it has not done so in an exaggerated manner with thousands of users connected at the same time, for example. That could cause this type of error and maybe others due to server and database load, but I don't think that's why, I'm not sure. The administrator could provide more information on this. So far it hasn't happened to me again so I guess it wasn't anything serious.
@Findingnemo please, if it happens again, write a post with details like the date, time and the browser you use so I can tell the administrator to take a look. Thank you.