I copied across all the files from my old host to my new one (the data dir, the config dir, the shell script I used to start the docker instance), then ran the same shell script to start it up (see below)
It grabbed the latest docker image successfully and it all came up: the same torrents, the same configuration.
But it wouldn't download at more than 5k, and even that was sporadic.
Then i killed that docker instance, and reran the docker run command, but instead of just the bare image name, I specified the old 2.0.5 version and it worked fine.
Then I skipped forward through the release versions until it stopped working and went back one, so I have the most recent version that works for me:
docker run -d \
--cap-add=NET_ADMIN \
-p 8112:8112 \
-p 8118:8118 \
-p 58846:58846 \
-p 58946:58946 \
--name=delugevpn \
-v /media/storage/fileshare:/data \
-v /home/delugevpnuser/docker/delugevpn/config:/config \
-v /etc/localtime:/etc/localtime:ro \
-e VPN_ENABLED=yes \
-e VPN_USER=xxxxxxxxxxxx \
-e VPN_PASS=yyyyyyyyyy \
-e VPN_PROV=pia \
-e VPN_CLIENT=openvpn \
-e STRICT_PORT_FORWARD=yes \
-e ENABLE_PRIVOXY=yes \
-e LAN_NETWORK=192.168.1.100/24,172.17.0.0/24,192.168.3.0/24 \
-e NAME_SERVERS=84.200.69.80,37.235.1.174,1.1.1.1,37.235.1.177,84.200.70.40,1.0.0.1 \
-e DELUGE_DAEMON_LOG_LEVEL=info \
-e DELUGE_WEB_LOG_LEVEL=info \
-e VPN_INPUT_PORTS=1234 \
-e VPN_OUTPUT_PORTS=5678 \
-e DEBUG=false \
-e UMASK=000 \
-e PUID=0 \
-e PGID=0 \
--restart=unless-stopped \
binhex/arch-delugevpn:2.1.1-1-02
I'm prepared to believe this is a ovpn config issue, but I've grabbed the latest files from PIA and compared it, there's no discernable change.
Edit to expand on this:
Version 2.1.1-1-02:
Version 2.1.1-4-01: