Client lost registered functions , and continue to publish

hi
i have a strange behaviour. i have a wamp client on a old (very slow) raspberry.
i can not call the registered topics:
$ wamp-cmd client.ping
2021-07-12T18:14:25+0200 ("ApplicationError(error=<wamp.error.no_such_procedure>, args=[‘no callee "
2021-07-12T18:14:25+0200 "registered for procedure <client.ping>’], kwargs={}, enc_algo=None, "
2021-07-12T18:14:25+0200 ‘callee=None, callee_authid=None, callee_authrole=None, forward_for=None)’)

but i still continue to receive its published messages

if i restart the client, everything goes back to normal
$ wamp-cmd client.ping
2021-07-12T18:19:18+0200 ‘pong’