the SG for this reads as
ip as-patch access-list 1 permit ^54
should it not be ^54$
My observation is that the ip as-path access-list is incorrect on both R4 and R6. Both regular expressions shown in the SG will match all prefixes received from AS54.
To select any prefix originated in AS54 it should be _54$ (remember prepending)
To select any prefix originated by a customer of AS54 it should be deny _54$; permit _54_