ObjectEditorIT#addingAndDeletingMultipleObjects is flickering

org.openqa.selenium.NoSuchElementException: 
Unable to locate element: #ObjectEditorIT\.NumberClass_1_number
For documentation on this error, please visit: https://www.seleniumhq.org/exceptions/no_such_element.html
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:17:03'
System info: host: '06b5a5543660', ip: '172.17.0.3', os.name: 'Linux', os.arch: 'amd64', os.version: '4.9.185-xxxx-std-ipv6-64', java.version: '1.8.0_282'
Driver info: org.openqa.selenium.remote.RemoteWebDriver
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: 384, moz:profile: /tmp/rust_mozprofile3tVrL0, moz:shutdownTimeout: 60000, moz:useNonSpecCompliantPointerOrigin: false, moz:webdriverClick: true, pageLoadStrategy: normal, platform: LINUX, platformName: LINUX, platformVersion: 4.9.185-xxxx-std-ipv6-64, rotatable: false, setWindowRect: true, strictFileInteractability: false, timeouts: {implicit: 0, pageLoad: 300000, script: 30000}, unhandledPromptBehavior: ignore, webdriver.remote.sessionid: a7a6369c-d1e5-4223-a39f-6b5...}
Session ID: a7a6369c-d1e5-4223-a39f-6b5f1d32f2d2
*** Element info: {Using=id, value=ObjectEditorIT.NumberClass_1_number}
	at sun.reflect.GeneratedConstructorAccessor89.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at org.openqa.selenium.remote.http.W3CHttpResponseCodec.createException(W3CHttpResponseCodec.java:187)
	at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:122)
	at org.openqa.selenium.remote.http.W3CHttpResponseCodec.decode(W3CHttpResponseCodec.java:49)
	at org.openqa.selenium.remote.HttpCommandExecutor.execute(HttpCommandExecutor.java:158)
	at org.openqa.selenium.remote.RemoteWebDriver.execute(RemoteWebDriver.java:552)
	at org.openqa.selenium.remote.RemoteWebElement.execute(RemoteWebElement.java:285)
	at org.openqa.selenium.remote.RemoteWebElement.findElement(RemoteWebElement.java:185)
	at org.openqa.selenium.remote.RemoteWebElement.findElementById(RemoteWebElement.java:221)
	at org.openqa.selenium.By$ById.findElement(By.java:188)
	at org.openqa.selenium.remote.RemoteWebElement.findElement(RemoteWebElement.java:181)
	at org.xwiki.test.ui.po.FormContainerElement.getFieldValue(FormContainerElement.java:95)
	at org.xwiki.flamingo.test.docker.ObjectEditorIT.addingAndDeletingMultipleObjects(ObjectEditorIT.java:240)