Got a C1037UN-EU box here. I'll try to run LE 005 and see if it has the same issue. You sure you have your video settings correct? Meaning the TV is auto-set for the correct video rate, and that audio is synced correctly?
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Well, I hate to disappoint you, but every testvideo I threw at my C1037 machine, it played it flawlessly, upto 4K 60fps h264. HEVC is only okay for most 720p rips on this box, but everything h264, mp2-4, interlaced/progressive... It plays it all and withouth stuttering in video or audio.
Try setting this right first WITHOUT the AV receiver. Connect your C1037 directly to your TV and see if you can get a clean, good working setup.