Without looking too deeply into this, one thought is to check your connection factory settings, and see if the (default) option of “send TextMessage using XML payload” is set to true. This might be causing your issue?
# show jndi connection-factory cf1 detail
Connection Factory : cf1
Message VPN : default
messaging-properties : 6
default-delivery-mode : persistent
text-msg-xml-payload : true <----
default-dmq-eligible : false
default-eliding-eligible : false
xa : false
jmsx-user-id-enabled : false
Are you using the most recent version of the Solace binder? I thought there might have been a fix for this recently…?