Why does the postgresql wal directory swell?

Question

PostgreSQL

The server falls under load from one of the databases. A data heap is inserted and a data heap is selected, after which more wal files are generated.

They are sent to the slave (there is monitoring of delays between the master and the slave) where they are successfully played.
They are archived, and there are no archiving errors (and there are no run-ups either, I monitor the number of wal not sent to the storage)

wal sooner or later overflows the disk and the server crashes, after which it reboots and the next checkpoint cuts all thousands of wal files without problems.
So far I think only in the direction of IO, because it is quite high. but I can't figure out why the wal is not being deleted, although it should be.