Pools and Persistence

You need an outer else clause for when the HTTP::uri does not start_with "/sc/" that resets the pool to the default pool:

when CLIENT_ACCEPTED {
   set default_pool [LB::server pool]
}
when HTTP_REQUEST {
   if { [HTTP::uri] starts_with "/sc/" } {
      ...
   } else {
      pool $default_pool
   }
}

Persistence has more to do with subsequent connections than with subsequent requests within the same keep-alive connection. The connection to the server is kept open until the pool selection actually changes (or OneConnect is configured).