First of all, this is the second time I've actually posted here, and you folks are right on the ball. Very impressive.
@c_schmitz : I see that the manual does say that now, but of course it didn't when I last read it. I guess it'd be an idea to check it again, especially after major version changes. I didn't think of the SMTP password, but it might be worth mentioning that no emails were being sent. It's an open survey, so no participant email address, and neither of the admin notifications is turned on. Anyhow, I'll restore the original LSSodium.php and try that for a non-kludgy fix.
@DenisChenu : That might be a good idea, but if you're just modifying it silently behind the scenes it wouldn't have helped me in this case. I basically have a zip of the stuff I need to restore, and I just delete everything except uploads, unzip the new version, and then unzip my stuff and overwrite where needed (templates, etc). Maybe I need to revisit this, but I have 5 installs going, so plucking individual files from sub-sub-sub folders (in the case of the templates) is pretty annoying. Now that I know to include security.php with my "stuff" to restore, I should be fine again, at least until the next change along these lines.
Anyhow, once again, thanks for being so quick with the solution.
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