Hello,
IT was good to hear that the command helped you to do away with the transparetn mode on SRX 300.
regarding your other concern please delete the vlan interfaces as you have already configured IRB interface and then check if you are able to get the ping working. You can delete the VLAN interfaces using the command "delete interfaces vlan".
If the ping still does not work please share the output of "show interfaces terse" from the SRX.
Thanks,
Pulkit Bhandari