ExtensionIT#testDowngrade is flickering

org.openqa.selenium.TimeoutException: 
Expected condition failed: waiting for org.xwiki.test.ui.XWikiWebDriver$$Lambda$451/1850680894@27bc13f4 (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: 'f3f4f6d1e0cf', 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: 74.0, javascriptEnabled: true, moz:accessibilityChecks: false, moz:buildID: 20200309095159, moz:geckodriverVersion: 0.26.0, moz:headless: false, moz:processID: 1083, moz:profile: /tmp/rust_mozprofileo5qy2o, 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: dismiss and notify}
Session ID: a186a9f8-0e80-46d6-9dce-5de6c2820215
	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.test.ui.XWikiWebDriver.waitUntilElementsAreVisible(XWikiWebDriver.java:330)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilElementsAreVisible(XWikiWebDriver.java:317)
	at org.xwiki.test.ui.XWikiWebDriver.waitUntilElementIsVisible(XWikiWebDriver.java:303)
	at org.xwiki.extension.test.po.ExtensionPane.clickAndWaitUntilElementIsVisible(ExtensionPane.java:180)
	at org.xwiki.extension.test.po.ExtensionPane.clickAndWaitForConfirmationOrJobDone(ExtensionPane.java:237)
	at org.xwiki.extension.test.po.ExtensionPane.clickAndWaitForConfirmationOrJobDone(ExtensionPane.java:223)
	at org.xwiki.extension.test.po.ExtensionPane.downgrade(ExtensionPane.java:330)
	at org.xwiki.test.ui.extension.ExtensionIT.testDowngrade(ExtensionIT.java:916)