Error is not very descriptive is it. This is all I see in the log you submitted:
Aug 18, 2017 15:45:00.982 [0x2b89a1200700] DEBUG - DVR:Grabber: Starting operation for ‘Star Trek - E24 - Turnabout Intruder’.
Aug 18, 2017 15:45:00.982 [0x2b89a1200700] DEBUG - Activity: registered new activity b14f5fc6-e63e-4218-ac3a-ca7dbbc5f86e - Recording
Aug 18, 2017 15:45:00.982 [0x2b899b001700] DEBUG - Completed: [10.0.0.39:59746] 200 GET /status/sessions/background (21 live) TLS GZIP 0ms 397 bytes (pipelined: 355)
Aug 18, 2017 15:45:00.982 [0x2b89a1200700] DEBUG - DVR:Grabber: HDHomerun starting a media grab on device device://tv.plex.grabbers.hdhomerun/13259206 (Silicondust HDHomeRun PRIME, supported) tuner 0.
Aug 18, 2017 15:45:00.983 [0x2b899ae00700] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Aug 18, 2017 15:45:00.983 [0x2b899ae00700] DEBUG - Auth: authenticated user 1 as Endda
Aug 18, 2017 15:45:00.983 [0x2b899ae00700] DEBUG - Auth: Came in with a super-token, authorization succeeded.
Aug 18, 2017 15:45:00.983 [0x2b89a2e06700] DEBUG - Request: [10.0.0.39:59747 (Allowed Network)] GET /status/sessions/background (20 live) TLS GZIP Signed-in Token (Endda)
Aug 18, 2017 15:45:00.983 [0x2b89a1200700] DEBUG - DVR:Subscription: Resolved subscription to library item ‘Star Trek’ (32142)
Aug 18, 2017 15:45:00.983 [0x2b899b001700] DEBUG - Completed: [10.0.0.39:59747] 200 GET /status/sessions/background (20 live) TLS GZIP 0ms 470 bytes (pipelined: 279)
Aug 18, 2017 15:45:00.984 [0x2b89b7c05700] DEBUG - DVR:Grabber: Freed a tuner (now 3 available)
Aug 18, 2017 15:45:00.984 [0x2b89b7c05700] DEBUG - DVR:Grabber: Recording for ‘Star Trek - E23 - All Our Yesterdays’ stopped with status cancelled.
Aug 18, 2017 15:45:00.984 [0x2b89b7c05700] DEBUG - DVR:Grabber: Scheduling ‘Star Trek - E23 - All Our Yesterdays’ for assimilation.
Aug 18, 2017 15:45:00.984 [0x2b89a380b700] DEBUG - DVR:Recorder: Asked to stop recording ‘Star Trek - E23 - All Our Yesterdays’.
Aug 18, 2017 15:45:00.985 [0x2b899b202700] DEBUG - DVR:Subscription: Resolved subscription to library item ‘Star Trek’ (32142)
Aug 18, 2017 15:45:00.985 [0x2b89a1200700] DEBUG - There were 1 top-level paths for Star Trek.
Aug 18, 2017 15:45:00.986 [0x2b89a1200700] DEBUG - DVR:Grabber: Saving recording to /DVR/.grab/7a3318be5377596e616fee0cdddbd7bf7a93823b
Aug 18, 2017 15:45:00.987 [0x2b899b202700] DEBUG - There were 1 top-level paths for Star Trek.
Aug 18, 2017 15:45:00.987 [0x2b899b202700] DEBUG - DVR:Grabber: Postprocessing, we’re going to put Star Trek - E23 - All Our Yesterdays in /DVR/Star Trek (1966)/Season 03/Star Trek (1966) - S03E23 - All Our Yesterdays.ts
Aug 18, 2017 15:45:00.988 [0x2b899b202700] DEBUG - DVR:Grabber: Moving /DVR/.grab/8f4087c929d624f4ab05b25fafff594d83412030/Star Trek (1966) - S03E23 - All Our Yesterdays.ts to /DVR/Star Trek (1966)/Season 03/Star Trek (1966) - S03E23 - All Our Yesterdays.ts
Aug 18, 2017 15:45:00.989 [0x2b89a7a02700] INFO - Library section 1 (TV Shows) will be updated because of a change in /DVR/Star Trek (1966)/Season 03
Aug 18, 2017 15:45:01.023 [0x2b899ae00700] DEBUG - Auth: We found auth token (xxxxxxxxxxxxxxxxxxxx), enabling token-based authentication.
Aug 18, 2017 15:45:01.023 [0x2b899ae00700] DEBUG - Auth: authenticated user 1 as Endda
Aug 18, 2017 15:45:01.023 [0x2b899ae00700] DEBUG - Auth: Came in with a super-token, authorization succeeded.
Aug 18, 2017 15:45:01.023 [0x2b89a6602700] DEBUG - Request: [10.0.0.39:59746 (Allowed Network)] GET /status/sessions/background (18 live) TLS GZIP Signed-in Token (Endda)
Aug 18, 2017 15:45:01.024 [0x2b899ae00700] DEBUG - Completed: [10.0.0.39:59746] 200 GET /status/sessions/background (18 live) TLS GZIP 0ms 397 bytes (pipelined: 356)
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Going to record for 4499 seconds, final URL is http://10.0.0.3:5004/auto/v756
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Setting timer to stop grab of ‘Star Trek - E24 - Turnabout Intruder’ in 4499 seconds.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Waiting for a tuner (3 available).
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Allocated a tuner (2 left)
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] ERROR - DVR:Recorder: Error 3 (The recording was aborted) starting the record, shutting things down.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Recorder: Asked to stop recording ‘Star Trek - E23 - All Our Yesterdays’.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Freed a tuner (now 3 available)
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] ERROR - DVR:Recorder: Error 3 (The recording was aborted) starting the record, shutting things down.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Recorder: Asked to stop recording ‘Star Trek - E23 - All Our Yesterdays’.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - DVR:Grabber: Operation for Star Trek - E24 - Turnabout Intruder completed with status error (The recording was aborted)
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] DEBUG - Activity: Ended activity b14f5fc6-e63e-4218-ac3a-ca7dbbc5f86e.
Aug 18, 2017 15:45:01.049 [0x2b89a1200700] ERROR - DVR:Grabber: Starting media grab failed.
As your Star Trek E23 is finishing Plex tries to start recording E24 which is aborted. No real error message to describe the error other than Error 3. Perhaps a Plex Employee @keithah or @BigWheel or a Plex Ninja @DaveBinM can provide some more insight into what an Error 3 is.