AttachmentIT.uploadAttachments is flickering

org.openqa.selenium.TimeoutException: 

Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:17:03'
System info: host: 'ca9368a6aa4b', ip: '172.17.0.2', os.name: 'Linux', os.arch: 'amd64', os.version: '4.19.0-13-cloud-amd64', java.version: '1.8.0_282'
Driver info: org.openqa.selenium.remote.RemoteWebDriver
Capabilities {acceptInsecureCerts: true, browserName: firefox, browserVersion: 86.0, javascriptEnabled: true, moz:accessibilityChecks: false, moz:buildID: 20210222142601, moz:geckodriverVersion: 0.29.0, moz:headless: false, moz:processID: 274, moz:profile: /tmp/rust_mozprofileUyBAp4, 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: 2e94e03e-82b5-450d-bc83-e8d...}
Session ID: 2e94e03e-82b5-450d-bc83-e8db08ec0bd4
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	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.click(RemoteWebElement.java:84)
	at org.xwiki.flamingo.test.docker.AttachmentIT.uploadAttachments(AttachmentIT.java:112)