IOS 14.4.1 doesn't work with NSAllowsLocalNetworking

I am testing an app with a service running HTTP (not HTTPS) on the local network with a port other than 80 . While Simulator works fine, testing on a device running 14.4.1 does not work even with NSAllowsLocalNetworking and NSAllowsArbitraryLoads set to true. Another device running 12.4.1 does work fine. The error does not indicate a problem with ATS per se.

App[291:4403] Task <4BD40346-63AA-405E-8D5F-951C35784434>.<1> HTTP load failed, 0/0 bytes (error code: -1009 [1:50])
2021-03-09 08:23:57.665602-0800 App[291:4404] Task <EE7BE7DD-7DFD-4E83-ACDE-F460E71C9929>.<2> HTTP load failed, 0/0 bytes (error code: -1009 [1:50])
2021-03-09 08:23:57.670428-0800 App[291:4406] Task <4BD40346-63AA-405E-8D5F-951C35784434>.<1> finished with error [-1009] Error Domain=NSURLErrorDomain Code=-1009 "The Internet connection appears to be offline." UserInfo={_kCFStreamErrorCodeKey=50, NSUnderlyingError=0x28277a430 {Error Domain=kCFErrorDomainCFNetwork Code=-1009 "(null)" UserInfo={_kCFStreamErrorCodeKey=50, _kCFStreamErrorDomainKey=1}}, _NSURLErrorFailingURLSessionTaskErrorKey=LocalDataTask <4BD40346-63AA-405E-8D5F-951C35784434>.<1>, _NSURLErrorRelatedURLSessionTaskErrorKey=(
"LocalDataTask <4BD40346-63AA-405E-8D5F-951C35784434>.<1>"
), NSLocalizedDescription=The Internet connection appears to be offline., NSErrorFailingURLStringKey=http://<internal_network>:5616/ios/user/, NSErrorFailingURLKey=http://<internal_network>:5616/ios/user/, _kCFStreamErrorDomainKey=1