When I click the Blue Ocean button, the blue line stops at about 7/8ths and nothing happens.

Chrome console:
blueocean.js:84447 Error starting Blue Ocean. TypeError: Cannot read property 'jenkinsConfig' of undefined
at Object.getSecurityConfig (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1324:22)
at Object.isJWTEnabled (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1327:21)
at Object.fetchJSON (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1564:31)
at ExtensionStore.extensionDataProvider (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84661:43)
at ExtensionStore._loadExtensionData (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7072:18)
at ExtensionStore._loadBundles (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7103:22)
at ExtensionStore.getExtensions (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7017:18)
at nextArg (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7010:32)
at ExtensionStore.getExtensions (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7013:17)
at Object.549../DevelopmentFooter (<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84928:30)__$$$_exec @ blueocean.js:84447_$$$__doBundleInit @ blueocean.js:84507545../init.jsx @ blueocean.js:84521s @ blueocean.js:1e @ blueocean.js:1(anonymous function) @ blueocean.js:1

Firefox console:
Error starting Blue Ocean. TypeError: config is undefined
Stack trace:
getSecurityConfig@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1324:9
isJWTEnabled@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1327:16
fetchJSON@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1564:14
extensionDataProvider@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84661:20
_loadExtensionData@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7072:13
_loadBundles@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7103:17
getExtensions@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7017:13
nextArg@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7010:25
getExtensions@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:7013:17
[549]<@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84928:1
s@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1:246
s/<@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1:305
[545]</__$$$__exec/<@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84444:9
[548]</exports.initialize@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84670:5
__$$$__exec@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84442:5
__$$$__doBundleInit@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84507:9
[545]<@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:84521:5
s@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1:246
e@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1:425
@<jenkins-url>/adjuncts/2693f0a3/io/jenkins/blueocean/blueocean.js:1:11
blueocean.js:84447:5
__$$$__exec()blueocean.js:84447
__$$$__doBundleInit()blueocean.js:84507
[545]<()blueocean.js:84521
s()blueocean.js:1
e()blueocean.js:1
<anonymní>blueocean.js:1