WDA v14.1.1 Has issues with MJPEG screenshots - SessionNotCreatedException

[tking16]

I'm using pytest-html to report on my test runs. For the iOS tests particularly I'm getting failures since upgrading my xcuitest and Appium. These failures aren't generating screenshots for my tests either:

 raise exception_class(message, screen, stacktrace)
E       selenium.common.exceptions.SessionNotCreatedException: Message: Could not start a new session. Could not start a new session. Error while creating session with the service http://localhost:4726. Could not start a new session. Response code 500. Message: Waited 10000ms but the MJPEG server never sent any images 
E       Host info: host: 'XD99WFXHKN', ip: '10.63.15.144'
E       Build info: version: '4.38.0', revision: '6b412e825c'
E       System info: os.name: 'Mac OS X', os.arch: 'aarch64', os.version: '26.2', java.version: '17.0.19'
E       Driver info: driver.version: unknown
E       Build info: version: '4.38.0', revision: '6b412e825c'
E       System info: os.name: 'Mac OS X', os.arch: 'aarch64', os.version: '26.2', java.version: '17.0.19'
E       Driver info: driver.version: unknown
E       Build info: version: '4.38.0', revision: '6b412e825c'
E       System info: os.name: 'Mac OS X', os.arch: 'aarch64', os.version: '26.4.1', java.version: '17.0.17'
E       Driver info: driver.version: unknown
E       Stacktrace:
E           at org.openqa.selenium.grid.node.remote.RemoteNode.newSession (RemoteNode.java:167)
E           at org.openqa.selenium.grid.distributor.local.LocalDistributor.startSession (LocalDistributor.java:427)
E           at org.openqa.selenium.grid.distributor.local.LocalDistributor.newSession (LocalDistributor.java:346)
E           at org.openqa.selenium.grid.distributor.local.LocalDistributor$NewSessionRunnable.handleNewSessionRequest (LocalDistributor.java:601)
E           at org.openqa.selenium.grid.distributor.local.LocalDistributor$NewSessionRunnable.lambda$run$1 (LocalDistributor.java:551)
E           at java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1136)
E           at java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:635)
E           at java.lang.Thread.run (Thread.java:840)

_env/lib/python3.14/site-packages/selenium/webdriver/remote/errorhandler.py:232: SessionNotCreatedException

Appium Server Log Snippet

[KazuCocoa]

It looks like the environment failed to take a screenshot, as there was no response from the underlying XCTest API.

�[38;5;131m[a18df869]�[0m�[38;5;101m[XCUITestDriver@3137]�[0m Starting MJPEG stream reading URL: 'http://localhost:9101'
�[38;5;131m[a18df869]�[0m�[38;5;173m[Xcode]�[0m 2026-06-17 09:26:42.079842+0100 WebDriverAgentRunner-Runner[86991:138061831] Error Domain=com.facebook.WebDriverAgent Code=1 "Cannot take a screenshot within 20000 ms timeout" UserInfo={NSLocalizedDescription=Cannot take a screenshot within 20000 ms timeout}
�[38;5;131m[a18df869]�[0m�[38;5;173m[Xcode]�[0m 2026-06-17 09:26:43.192752+0100 WebDriverAgentRunner-Runner[86991:138061831] Error Domain=com.facebook.WebDriverAgent Code=1 "Cannot take a screenshot within 20000 ms timeout" UserInfo={NSLocalizedDescription=Cannot take a screenshot within 20000 ms timeout}
�[38;5;131m[a18df869]�[0m�[38;5;85m[Support]�[0m Error getting MJpeg screenshot chunk: aborted
�[38;5;131m[a18df869]�[0m�[38;5;85m[Support]�[0m The connection to MJPEG server at http://localhost:9101 has been closed

WebDriverAgent/WebDriverAgentLib/Utilities/FBScreenshot.m

Lines 110 to 132 in 417db80

	[proxy _XCT_requestScreenshot:screnshotRequest
	withReply:^(id image, NSError *err) {
	if (nil != err) {
	innerError = err;
	} else {
	screenshotData = [image data];
	}
	dispatch_semaphore_signal(sem);
	}];
	int64_t timeoutNs = (int64_t)(timeout * NSEC_PER_SEC);
	if (0 != dispatch_semaphore_wait(sem, dispatch_time(DISPATCH_TIME_NOW, timeoutNs))) {
	NSString *timeoutMsg = [NSString stringWithFormat:@"Cannot take a screenshot within %@ timeout", formatTimeInterval(SCREENSHOT_TIMEOUT)];
	if (nil == error) {
	[FBLogger log:timeoutMsg];
	} else if (nil == innerError) {
	[[[FBErrorBuilder builder]
	withDescription:timeoutMsg]
	buildError:error];
	}
	}
	if (nil != error && nil != innerError) {
	*error = innerError;
	}

What was printed in the device log?

Also, what version was working? The latest version's changes were log messages/docstring #1154