You are using a server from 2009 year (post from end 2010, they changed only protocols for newer tibia). As I remember, more popular was The Forgotten Server Crying Damson. Becouse it has less bugs. Crying Damson was updated more frequently and I recommend to use
TFS Crying Damson 0.3.6 or
0.4. Both versions are for Tibia 8.6, your OTS is for Tibia 8.62, this little downgrade wont change anything.
This what I got after searching
this.
As you see alot of people had exactly the same problem with
TFS Mystic Spirit 0.2.8. Becouse server's engine, which are you using is bugged. From all infos, I found this thread with temporary solution (look at creation date)
https://otland.net/threads/quest-rewards-trouble.122734/. But I highly recommend to do an upgrade to TFS 0.3.6 or 0.4.