cherry picking.

By default, routers do not retain access logs, and permanently delete messages and queues when requested. Messages persist in memory or in a database until they cross a threshold of time, typically on the order of days.[0] There is still a risk that a router maliciously records all queues and messages (even though encrypted) sent via the same transport connection to gain a partial knowledge of the user's communications graph and other meta-data.

what this means is don't blindly trust a random public router.

if you host your own router, you can set the threshold to hours or seconds. you can also ensure that your router isn't maliciously storing records.

simplex uses an in-memory queue to store messages for delivery. if the server was extracted for legal measures, this means the messages are erased and difficult if not impossible to collect.

for signal, they are written to disk. this means there is evidence of communications between users. even if you host your own signal server, it will be there.