There is a limitation in CX3. Your line size (In number of bytes) should be exactly divisible by 3. This is because the MIPI block's internal buffer can not pad zeros and send the additional 8-bit pixel to align with 24-bit bus width.
To answer your question, we have seen that the DATA_COUNT is unpredictable in such cases and it becomes very hard to debug. So your sensor should send 1599/1602 pix in a line as this is divisible by 3.
Also note that you can use a 2-byte format like UYVY and hence you will not have such issues as the line width (1600) is divisible by 2. But the only drawback is that the max. throughput will be 2*100 MBps as the max clock is 100MHz and not 300MBps (When you use RGB888 format, 3 bytes per clock).