Sorry, I know that bug reports are not supposed to come here but I didn't find any better place. Let's hope the developer reads the users' reports.
First known bad: UA:"Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0 SeaMonkey/2.51a1" ID:20170306145452 en-US c-c:8be1ae77d2644e401fa6480a05ff234e70d0ccdf m-c:b7e42143bbbc9dc3e5c05bd1e93b6485ce1d0ad4
Last known good: 20170306003001 http://hg.mozilla.org/comm-central/rev/495489dbbfa52f82c5b82abddd2256219aabbc2c http://hg.mozilla.org/mozilla-central/rev/8d026c601510 Same UA and localization (or lack thereof) as above, except that the "last good" build had Firefox 54.0a1 with SeaMonkey 2.51a1 which is more normal.
Using Addons Recent Updates 0.1.7 in both cases.
Symptom: Even though the extension's pref is set to 366 days, I only see a couple of days' worth of updates in about:addons
Best regards, Tony.
*Edit* After installing the development version from https://github.com/Infocatcher/Addons_Recent_Updates/ it works again (see details on the issues page mentioned in the developer's reply).
This review is for a previous version of the add-on (0.1.7).