First I would use summitX-21.1.3.7-patch1-7.xos or (in my Opinion better) summitX-21.1.5.2-patch1-5.xos
The plain summitX-21.1.3.7.xos has some bugs, that might affect you.
What are you pinging with .216, as I can''t find that IP in your scheme?
If you can, please do a "show log" if it doesn't work with this versions and post the output here.
I wouldn't recommend using the Default VLAN, although it might work.
Using an untagged (=> Access port!) VLAN between two switches shouldn't be used in favor to using tagged vlans (=> trunk).
If you still want to use it you should configure:
code:configure vlan Default delete ports 24
configure vlan Default add ports 24 tagged
(but shouldn't be a serious impact here)