These bugs appear to be caused by the LastPass extension.
Final update: I have been able to work around this issue by adding Kegland.com.au as a "Never AutoLogin" URL per this page:
Manage Never URLs
Make sure to add it as "kegland.com.au" rather than "
www.kegland.com.au/" - the first will apply to the whole domain, the second to only the homepage.
Hooray, the Kegland website is usable again!
I think these are Chrome bugs - they happen to me every time on my primary install of Chrome (81.0.4044.138) but I can't reproduce the behaviour on Chrome Canary (85.0.4156.0), Firefox , pre-Chromium Edge (44.18362.449.0), or IE 11.
Which is all good and well, but apparently means the web devs they've employed (MITASH) don't test their sites on the current stable version of the world's most popular browser, which is pretty wild.
EDIT: Actually, I can't reproduce the behaviour on a clean profile of Chrome, either. Looks like I need to figure out which one of my extensions is interfering...