Oddly, it feels like others editing for a very long time participating in the discussions do not remember a mass problem—or at least not one so acute and widespread to be worth bringing up in the two discussions thus far, only a concern about copy-editing and housekeeping. Are there logs or a number of page histories pointing to incidents of widespread vandalism problems acute enough have triggered the decision? Was it sustained constant tide of vandalism, or one-time one-user incidents every couple of weeks? What exactly what the incident that finalized the decision to turn off unregistered editing? What was the final nail in the coffin?
And, for that matter, what do "problematic" and "issues" mean in the context? Is it all vandalism and trolling—or, does it include malformed formatting, innocent narrative misunderstandings, and forgetting to add in references? Understanding the decision requires clarity on this.
Why have you felt long-term semi-protection of common targets, both at the editing level and the commenting level, to fail as a solution to curtailing the problem? Outside of protections related to the Fandom move, there have only been 15 page protections, usually of short duration. And looking at the histories for those pages, it seems to have curtailed the issue effectively. Overall, why has indef semi-protection of pages been not considered before turning off unregistered editing?
The block log shows only about 16 blocks of unregistered users related to vandalism, edit warring, trolling, spam, or hate speech over the past year of unregistered editing, which also does not feel to be in line with a characterization of a mass problem requiring turning off unregistered editing. (Also, those four blocks to try to force account creation to explain basic guidance, however, is arguably bordering on abuse of the block function even with the consideration of "it's difficult to communicate with IP editors"? Especially given the absence of style or conventions guides?)
Take into account that there are no accessible centralized guidelines, real explanation on this wiki of what good editing behavior and formatting looks like, little conversation being held on ANY talk pages. There isn't even an page to link the phrase "rules for attribution" in the rules to. Would the development of a centralized style guideline curtail any of these issues? It's my experience, looking at new registered editors that badly formed but good faith edits here at the wiki are the result of the complete lack of style guidelines.
Yes, barrier to entry isn't high for regular editing—but creating an account is high enough when one wants to make a spelling or grammar correction, or some other minor edit only once in a while.
And, again, about unregistered editing being made available on July 15 and July 16, then turned off again despite lack of major incident. What's the story there?
There are a number of tools that this wiki has not at all used that are developed specifically to address these problems. And, looking at page histories and logs, they appear adequate for the problems observed there: has it been considered to institute content moderators (of which there are none) to help protect pages targeted by vandalism, thread moderators (of which there are none) to manage trolling in comments, and rollbacks (of which there are none) to quickly undo vandalism? Has it been considered turning on the Recent Changes patrol log? Has a boilerplate editing notice explaining basic referencing guidelines and style conventions, perhaps linking to a central guide, been considered for its merits as a means of communicating practices?
Perhaps in tandem with the above tools, will the development of a centralized style and best local practices be taken into consideration on opening up unregistered editing again, even as a test run of a handful of weeks?