Here's the anonymized end of owncloud.log (still cannot upload the file, so I'll copy-paste it in here, apologies for the mess):
{"reqId":"XXX1","remoteAddr":"111.222.333.444","app":"core","message":"starting upgrade from 8.2.0.12 to 8.2.10.2","level":0,"time":"2017-03-18T20:16:26+00:00","method":"GET","url":"\/oc\/core\/ajax\/update.php?requesttoken=Q1"}
{"reqId":"XXX1","remoteAddr":"111.222.333.444","app":"no app in context","message":"Exception: {\"Exception\":\"Symfony\\\\Component\\\\Routing\\\\Exception\\\\RouteNotFoundException\",\"Message\":\"Unable to generate a URL for the named route \\\"calendar_index\\\" as such route does not exist.\",\"Code\":0,\"Trace\":\"#0 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/route\\\/router.php(325): Symfony\\\\Component\\\\Routing\\\\Generator\\\\UrlGenerator->generate('calendar_index', Array, false)\\n#1 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/urlgenerator.php(65): OC\\\\Route\\\\Router->generate('calendar_index', Array)\\n#2 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/helper.php(66): OC\\\\URLGenerator->linkToRoute('calendar_index', Array)\\n#3 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/public\\\/util.php(301): OC_Helper::linkToRoute('calendar_index', Array)\\n#4 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/apps\\\/calendar\\\/appinfo\\\/app.php(25): OCP\\\\Util::linkToRoute('calendar_index')\\n#5 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(160): require_once('\\\/homepages\\\/YY\\\/d...')\\n#6 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(141): OC_App::requireAppFile('calendar')\\n#7 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(1171): OC_App::loadApp('calendar', false)\\n#8 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/installer.php(222): OC_App::updateApp('calendar')\\n#9 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/installer.php(252): OC_Installer::updateApp(Array)\\n#10 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(506): OC_Installer::updateAppByOCSId('168707')\\n#11 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(320): OC\\\\Updater->upgradeAppStoreApps(Array)\\n#12 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(202): OC\\\\Updater->doUpgrade('8.2.10.2', '8.2.0.12')\\n#13 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/core\\\/ajax\\\/update.php(111): OC\\\\Updater->upgrade()\\n#14 {main}\",\"File\":\"\\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/3rdparty\\\/symfony\\\/routing\\\/Symfony\\\/Component\\\/Routing\\\/Generator\\\/UrlGenerator.php\",\"Line\":134}","level":3,"time":"2017-03-18T20:16:31+00:00","method":"GET","url":"\/oc\/core\/ajax\/update.php?requesttoken=KK%LL"}
{"reqId":"XXX1","remoteAddr":"111.222.333.444","app":"no app in context","message":"Exception: {\"Exception\":\"Symfony\\\\Component\\\\Routing\\\\Exception\\\\RouteNotFoundException\",\"Message\":\"Unable to generate a URL for the named route \\\"contacts_index\\\" as such route does not exist.\",\"Code\":0,\"Trace\":\"#0 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/route\\\/router.php(325): Symfony\\\\Component\\\\Routing\\\\Generator\\\\UrlGenerator->generate('contacts_index', Array, false)\\n#1 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/urlgenerator.php(65): OC\\\\Route\\\\Router->generate('contacts_index', Array)\\n#2 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/helper.php(66): OC\\\\URLGenerator->linkToRoute('contacts_index', Array)\\n#3 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/public\\\/util.php(301): OC_Helper::linkToRoute('contacts_index', Array)\\n#4 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/apps\\\/contacts\\\/appinfo\\\/app.php(18): OCP\\\\Util::linkToRoute('contacts_index')\\n#5 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(160): require_once('\\\/homepages\\\/YY\\\/d...')\\n#6 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(141): OC_App::requireAppFile('contacts')\\n#7 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(1171): OC_App::loadApp('contacts', false)\\n#8 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/installer.php(222): OC_App::updateApp('contacts')\\n#9 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/installer.php(252): OC_Installer::updateApp(Array)\\n#10 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(506): OC_Installer::updateAppByOCSId('168708')\\n#11 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(320): OC\\\\Updater->upgradeAppStoreApps(Array)\\n#12 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/updater.php(202): OC\\\\Updater->doUpgrade('8.2.10.2', '8.2.0.12')\\n#13 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/core\\\/ajax\\\/update.php(111): OC\\\\Updater->upgrade()\\n#14 {main}\",\"File\":\"\\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/3rdparty\\\/symfony\\\/routing\\\/Symfony\\\/Component\\\/Routing\\\/Generator\\\/UrlGenerator.php\",\"Line\":134}","level":3,"time":"2017-03-18T20:16:36+00:00","method":"GET","url":"\/oc\/core\/ajax\/update.php?requesttoken=KK%LL"}
{"reqId":"XXX2","remoteAddr":"111.222.333.444","app":"index","message":"Exception: {\"Exception\":\"OC\\\\NeedsUpdateException\",\"Message\":\"\",\"Code\":0,\"Trace\":\"#0 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php(117): OC_App::loadApp('files')\\n#1 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/util.php(142): OC_App::loadApps(Array)\\n#2 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/base.php(906): OC_Util::setupFS()\\n#3 \\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/index.php(47): OC::handleRequest()\\n#4 {main}\",\"File\":\"\\\/homepages\\\/YY\\\/UU\\\/htdocs\\\/oc\\\/lib\\\/private\\\/app.php\",\"Line\":142}","level":3,"time":"2017-03-18T20:29:08+00:00","method":"GET","url":"\/oc\/index.php\/core\/js\/oc.js?v=OO","user":"--"}
{"reqId":"XXX3","remoteAddr":"111.222.333.444","app":"core","message":"starting upgrade from 8.2.10.2 to 9.0.8.2","level":0,"time":"2017-03-18T20:29:14+00:00","method":"GET","url":"\/oc\/core\/ajax\/update.php?requesttoken=BBBB","user":"--"}
{"reqId":"XXX3","remoteAddr":"111.222.333.444","app":"core","message":"No update found at the ownCloud appstore for app 166054","level":0,"time":"2017-03-18T20:29:17+00:00","method":"GET","url":"\/oc\/core\/ajax\/update.php?requesttoken=BBBB","user":"--"}
I hope someone can make anything out of this?