Experiencing strange problem.
Im running an x4r sb on my qav 220.
Today I my quad lost signal. This was the second time this has happened in a month of flying, so it is rare.
It is not a distance problem as this has occurred within 30m on both occasions.
I still have video but the control just disappearsand did not receive any warning from my Taranis.
After getting the quad back it flys again without problems.
This is driving me nuts and Im losing confidence in my rig.
Any suggestions?

X4rsb, Xracer f3, Matek hubosd. Unify pro hv.

I am facing same problem with X6R. After 25-30m it start giving RSSI warnings of low singnal and critical signal. Any specific reason?

I don't think your problem is the same as mine. Your getting RSSI warnings, which I dont. My quad just falls out of the sky without any warning.

Have you guys checked the receiver antenna cables. Hope they are not frayed... if all looks ok, try with another receiver to isolate tx end issues.

Antenna wires should be approx 31mm length

I have heard that carbon fiber absorbs signal. might that may be the problem,if your frame is made out of it. not sure though.

A 220 size would be too small to shield any signals.
Usually the antennas hang out loose outside the frame. That is one of the reasons for snapped or frayed rx wires.

how are you powering ?

thru the flight battery ?

power with a seperate battery and isolate the flight battery only for the motors
( just as a test)
loss of signal intermittently is usually due to power glitch ... most likely the
switching regulators on the pdb

If a quad falls out without RSSI failsafe, we can eliminate doubt on RSSI. It is usually one of the following:
1. Motor-ESC desync
2. When you do an aggressive throttle punch out, there is too much of a voltage sag and electrical noise for an instant, resulting in flight controller getting reset. Adding a capacitor on the XT60 connector gives some resort. 1000uF 35V radial electrolytic capacitor serves good for me so far.
3. Recheck all your wirings for cold solder and loose connectors.

Do you have blackbox logging on your setup? What motors and ESCs do you use?

If the receiver antenna has too many cuts all over its body, its probably time to replace the antenna. If only the edge of the antenna is damaged, cut the exposive part out and make a new exposive part of same length.

Make sure that the exposive part of the receiver antenna(the last -3cm) is nice and straight(ie. neither chopped nor bent). Also ensure that the exposive part is well clear of carbon fiber frame.

Thanks guys for your help. Firstly, the RX is powered from the Fc and the Fc is powered from the PDB/OSD. I already have the 1000/35v Cap installed but on both occasions when this problem occurred, I was just cruising around at around 12-15 amps.
After doing a little research I found this:     
Here Joshua Bardwell explains pretty much what it could be.
After watching the video I did some changes to the quad. I got rid of the remaining connectors and pretty much soldered everything directly. I also relocated the Rx to a more open space.
Will test today and get back to you guys.

Regards Ashim.