Sudden amplitude jumps in data captured with AD9208-3000EBZ.

Hi, I'm capturing data with AD9208-3000EBZ and a custom FPGA receiver board. The problem is that I see abrupt changes in captured signal level.

The AD9208 configuration is:

1. Sample rate is 3GSps.

2. 1 DDC enabled, real input (only from channel A), complex output, decimate by 4.

3. DDC's NCO in ZIF mode.

4. JESD is set to operate in Subclass 0 mode. (L, M, F) = [2, 2, 2], N=16, N'=16. Resulting lane rate is 15Gbps.

I use 10MHz signal as an AD9208 input.

This is how captured data looks like:

But when I enable various test modes, I see no such jumps.

Ramp test mode output (reg 0x0550 = 0x0F, reg 0x0327 = 0x05):

1/0-word toggle test mode output (reg 0x0550 = 0x07, reg 0x0327 = 0x05):

Output when NCO IF = 10MHz with enabled test mode:

What can be the reason of this? I tested two signal generators as input sources and this problem exists in both cases.

Thank you!