RegisterIT#registerExistingUser is flickering

org.openqa.selenium.NoSuchElementException: 
no such element: Unable to locate element: {"method":"css selector","selector":"#register"}
  (Session info: chrome=120.0.6099.224)
For documentation on this error, please visit: https://www.selenium.dev/documentation/webdriver/troubleshooting/errors#no-such-element-exception
Build info: version: '4.16.1', revision: '9b4c83354e'
System info: os.name: 'Linux', os.arch: 'amd64', os.version: '4.19.0-16-cloud-amd64', java.version: '17.0.9'
Driver info: org.openqa.selenium.remote.RemoteWebDriver
Command: [059f01bea166458f11d7c626455339db, findElement {using=id, value=register}]
Capabilities {acceptInsecureCerts: false, browserName: chrome, browserVersion: 120.0.6099.224, chrome: {chromedriverVersion: 120.0.6099.109 (3419140ab66..., userDataDir: /tmp/.org.chromium.Chromium...}, fedcm:accounts: true, goog:chromeOptions: {debuggerAddress: localhost:42049}, goog:loggingPrefs: {browser: ALL}, networkConnectionEnabled: false, pageLoadStrategy: normal, platformName: linux, proxy: Proxy(), se:bidiEnabled: false, se:cdp: ws://172.17.0.7:4444/sessio..., se:cdpVersion: 120.0.6099.224, se:vnc: ws://172.17.0.7:4444/sessio..., se:vncEnabled: true, se:vncLocalAddress: ws://172.17.0.7:7900, setWindowRect: true, strictFileInteractability: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: ignore, webauthn:extension:credBlob: true, webauthn:extension:largeBlob: true, webauthn:extension:minPinLength: true, webauthn:extension:prf: true, webauthn:virtualAuthenticators: true}
Session ID: 059f01bea166458f11d7c626455339db
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at org.openqa.selenium.remote.codec.w3c.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:200)
	at org.openqa.selenium.remote.codec.w3c.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:133)
	at org.openqa.selenium.remote.codec.w3c.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:52)
	at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:191)
	at org.openqa.selenium.remote.TracedCommandExecutor.execute(TracedCommandExecutor.java:51)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:523)
	at org.openqa.selenium.remote.ElementLocation$ElementFinder$2.findElement(ElementLocation.java:165)
	at org.openqa.selenium.remote.ElementLocation.findElement(ElementLocation.java:59)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:360)
	at org.openqa.selenium.remote.RemoteWebDriver.findElement(RemoteWebDriver.java:354)
	at org.xwiki.test.ui.XWikiWebDriver.findElement(XWikiWebDriver.java:714)
	at org.xwiki.test.ui.XWikiWebDriver.findElementWithoutWaiting(XWikiWebDriver.java:84)
	at org.xwiki.test.ui.po.FormContainerElement.<init>(FormContainerElement.java:54)
	at org.xwiki.test.ui.po.AbstractRegistrationPage.getForm(AbstractRegistrationPage.java:95)
	at org.xwiki.test.ui.po.AbstractRegistrationPage.fillRegisterForm(AbstractRegistrationPage.java:89)
	at org.xwiki.administration.test.ui.RegisterIT.registerExistingUser(RegisterIT.java:259)