HMC624A attenuator power up for direct parallel mode problem

This circuit is powered up by VCCRXMIX=4.5V with Dx=0V. After 100us I set Dx into desired state. Dx levels is 3.3V CMOS.

But I see -30dB attenuation after power up within ~5ms independent of Dx levels. After 5ms attenuation becomes normal.

What am I doing wrong?

No problem with still power in pin 18.
[edited by: neon416 at 10:05 PM (GMT -5) on 25 Nov 2020]