Three questions about Postgres Logical Replication

This is Jack from Lenovo. I experienced some problems when using Postgres Logical Replication.
Would you like to help me answer those question ? Thanks

Env: PostgreSQL 10.5
OS: Centos 6.9

1: There is a server which has been configured 13 publications.
All subscriptions configured on others server.
The publication and subscriptions service running well.
I found this directory have a lot of file. "/data/pg_logical/snapshots"

The number of log files grows over time. I could reproduce this scenario on test environment.
[postgres(at)bljcxjb3h4 snapshots]$ find /data/postgres/instance01/data/pg_logical/snapshots -type f | wc -l
783895

-rw------- 1 postgres postgres 144 Jun 3 14:36 0-300007A8.snap
-rw------- 1 postgres postgres 144 Jun 3 14:36 0-300007E0.snap
-rw------- 1 postgres postgres 144 Jun 3 14:36 0-30000888.snap
-rw------- 1 postgres postgres 144 Jun 4 23:00 0-30000AA8.snap

Could I know why this directory exist those file ? Could I manually delete those file ?

2: Recently. Our server restart unexpected. A file corrupt after server restart.
Follow in is logs.
CST,,0,PANIC,58P01,"replication slot file ""pg_replslot/f37tt19/state"" has wrong magic number: 1369563137 instead of 17112225",,,,,,,,,""
CST,,0,LOG,00000,"startup process (PID 3663) was terminated by signal 6: Aborted",,,,,,,,,""
CST,,0,LOG,00000,"aborting startup due to startup process failure",,,,,,,,,""
CST,,0,LOG,00000,"database system is shut down",,,,,,,,,""
Look like a replication slot file corrupt. This file corrupt block database activation.
I have to restore entire database to resolve this problem.
Is there any others workaround to resolve this problem ? Actually I expect to start database then rebuild logical replication.

3: Currently. Logical replication automatic start with database activation .DBA unable to control it.
I suggest start/stop it independent.