Audio out of sync in Source window

Edit panel, source window.

TL is 1080p23.976. source material is C300mk1 & mk2 1080 & 2K 23.976

10.13.4+secruity update, MP 2X6 core 3.48G, titan x

Audio Hardware : tascam 20X20 USB interface @ 96K with external word clock lock set as system playback, R15 set to use system sound, Sumo19 SDI monitor fed via 4K extreme card

Play source clip and audio drifts out rather quickly. Sync is bad between system audio out and both computer monitor and SDI out. picture sync between computer and SDI looks to be within a frame Audio on SDI is good and if you have it turned out its easy to hear the system sound out drifting away by many seconds across a 1 minute play. clips themselves are 5-20min long, their sync is good.

playback in timeline set to 1080p23.976 is good. the only problem is source window

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UPDATE : sync is also out when playing TL on Usb interface. SDI audio looks good.

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