With 4K LUKS sectors the write speed is too low for a modern SSD. Check that LUKS use a fast implementation. I have:
$ /usr/sbin/cryptsetup benchmark ... # Algorithm | Key | Encryption | Decryption aes-cbc 128b 664.1 MiB/s 2615.9 MiB/s
and my LUKS setup uses aes-xts 512b.
With 4K LUKS sectors the write speed is too low for a modern SSD. Check that LUKS use a fast implementation. I have:
... aes-xts 512b 2708.8 MiB/s 2986.0 MiB/sand my LUKS setup uses aes-xts 512b.