OpenWRT 19: ssh_exchange_identification: Connection closed by remote host

After upgrading some devices to a build based on OpenWRT 19.07, revision r11325-616fff2a94, once the sysupgrade finishes, trying to connect via SSH from the management VPN to devices gives me this error:

ssh_exchange_identification: Connection closed by remote host

-v output:

OpenSSH_7.9p1 Debian-10+deb10u2, OpenSSL 1.1.1d  10 Sep 2019
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolve_canonicalize: hostname [ip] is address
debug2: ssh_connect_direct
debug1: Connecting to [ip] [[ip]] port 22.
debug1: Connection established.
debug1: identity file /root/.ssh/id_rsa type 0
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: identity file /root/.ssh/id_dsa type -1
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: identity file /root/.ssh/id_xmss type -1
debug1: identity file /root/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
ssh_exchange_identification: Connection closed by remote host

Connecting via LAN works.
After a while the problem goes away and I'm able to get in also via the management VPN, but may re-appear intermittently shortly afterwards.

If I reboot the device, I don't see the problem anymore.

I could ignore it but it's a bit worrying, I had not seen this behavior before on previous versions.
Is anybody else experiencing the same issue?