OP is using H.265 encoding, best practices are to use plain H.264, not H.264B, not H.264H. And IMHO, don't mix encoders (some cams H.264, some cams H.265), Blue Iris doesn't seem to tolerate that well. All cameras set to H.264. Use CBR, match FPS and iframe. Set at least 8192 Mb/s for 8MP.
Do...