Test FlamingoThemeIT#validateColorThemeFeatures is flickering

org.openqa.selenium.TimeoutException: 
Expected condition failed: waiting for org.xwiki.test.ui.XWikiWebDriver$$Lambda$918/1913176634@3bcc3d07 (tried for 10 second(s) with 500 milliseconds interval)
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:17:03'
System info: host: 'b19df4700702', ip: '172.17.0.2', os.name: 'Linux', os.arch: 'amd64', os.version: '4.19.0-13-cloud-amd64', java.version: '1.8.0_242'
Driver info: org.xwiki.test.ui.XWikiWebDriver
Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 76.0.1, javascriptEnabled: true, moz:accessibilityChecks: false, moz:buildID: 20200507114007, moz:geckodriverVersion: 0.26.0, moz:headless: false, moz:processID: 241, moz:profile: /tmp/rust_mozprofileNvadpN, moz:shutdownTimeout: 60000, moz:useNonSpecCompliantPointerOrigin: false, moz:webdriverClick: true, pageLoadStrategy: normal, platform: LINUX, platformName: LINUX, platformVersion: 4.19.0-13-cloud-amd64, rotatable: false, setWindowRect: true, strictFileInteractability: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: ignore, webdriver.remote.sessionid: 63c40e8c-a485-45b9-9782-c02...}
Session ID: 63c40e8c-a485-45b9-9782-c02e96336e6f
	at org.openqa.selenium.support.ui.WebDriverWait.timeoutException(WebDriverWait.java:95)
	at org.openqa.selenium.support.ui.FluentWait.until(FluentWait.java:272)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilCondition(XWikiWebDriver.java:228)
	at org.xwiki.flamingo.test.po.EditThemePage.waitUntilReady(EditThemePage.java:132)
	at org.xwiki.flamingo.test.po.EditThemePage.<init>(EditThemePage.java:43)
	at org.xwiki.flamingo.test.po.ThemeApplicationWebHomePage.createNewTheme(ThemeApplicationWebHomePage.java:77)
	at org.xwiki.flamingo.test.ui.FlamingoThemeIT.validateThemeCreation(FlamingoThemeIT.java:112)
	at org.xwiki.flamingo.test.ui.FlamingoThemeIT.validateColorThemeFeatures(FlamingoThemeIT.java:98)