Same issue here. Just tried to install resilio-sync (2.6.1-1) on ubuntu MATE 19.04.
$ systemctl status resilio-sync.service
● resilio-sync.service - Resilio Sync service
Loaded: loaded (/lib/systemd/system/resilio-sync.service; enabled; vendor pre
Active: activating (start) since Thu 2019-04-25 20:22:47 CEST; 35s ago
Docs: https://help.resilio.com
Tasks: 15 (limit: 4915)
Memory: 4.2M
CGroup: /system.slice/resilio-sync.service
└─5204 /usr/bin/rslsync --config /etc/resilio-sync/config.json
Apr 25 20:22:47 pocket systemd[1]: Starting Resilio Sync service...
Apr 25 20:22:47 pocket systemd[1]: resilio-sync.service: Can't open PID file