If problem still persist after upgrading firmware, it probably there are no changes made to the P2P client in the new firmware release.
My personal advice is to switch to alternative BT client like Transmission, it save you a lot of headache and is widely used even for private site.
i've already installed Transmission client on my nas, but the results are the same. The CPU 100% and the downloads still blocked.
I've a strange problem in transmission.daemon.log (please see below a little part of it), when i start the transmission service, the log file grows until i stop the service. The crypto error repeats...
[23:50:44.890] Transmission 2.80 (14103) started (session.c:737)
[23:50:44.890] RPC Server Adding address to whitelist: 127.0.0.1 (rpc-server.c:828)
[23:50:44.890] RPC Server Adding address to whitelist: 192.168.*.* (rpc-server.c:828)
[23:50:44.891] RPC Server Serving RPC and Web requests on port 127.0.0.1:9091/transmission/ (rpc-server.c:1035)
[23:50:44.891] RPC Server Whitelist enabled (rpc-server.c:1039)
[23:50:44.891] RPC Server Password required (rpc-server.c:1042)
[23:50:44.891] DHT Generating new id (tr-dht.c:310)
[23:50:44.891] tr_crypto error:00000000:lib(0):func(0):reason(0) (crypto.c:342)
[23:50:44.891] tr_crypto error:00000000:lib(0):func(0):reason(0) (crypto.c:342)
[23:50:44.892] Using settings from "/mnt/HD/HD_a2/.transmission-daemon" (daemon.c:526)
[23:50:44.892] Saved "/mnt/HD/HD_a2/.transmission-daemon/settings.json" (variant.c:1217)
[23:50:44.892] transmission-daemon requiring authentication (daemon.c:546)
[23:50:44.892] Loaded 2 torrents (session.c:1976)
[23:50:44.892] Port Forwarding (NAT-PMP) initnatpmp succeeded (0) (natpmp.c:73)
[23:50:44.892] Port Forwarding (NAT-PMP) sendpublicaddressrequest succeeded (2) (natpmp.c:73)
[23:50:52.970] Port Forwarding Starting (port-forwarding.c:95)
[23:50:52.970] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.970] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.971] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.972] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.973] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.974] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.975] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.976] tr_crypto error:24064064:lib(36):func(100):reason(100) (crypto.c:115)
[23:50:52.976] tr_crypto error:24064064:lib(36):func(100):reason(100)