Hello,
Have you rebooted the SRX after configuring the IRB interface.
If not then please reboot it and check if it works becasue When we configure a device as Ethernet switch , the mode changes to mix mode and during commit a warning will be seen for a reboot so we need to also reboot the SRX for this configuration to take effect.
Thanks,
Pulkit Bhandari
Please mark my response as Solution Accepted if it Helps, Kudos are Appreciated too. 