In the early 70s I was in AF comms and worked extensively with HF, VHF, UHF and EHF communications and radar equipment.
In that time, we experienced a SID (sudden ionospheric disturbance) that knocked out about all of our comms. It (ionospheric disturbance) cause by solar sunspot/flare activity where large volumes of the earth’s ionosphere is ionized by the radiation. It effectively is a big sponge for long haul communications, especially those that depended on the normal environment of the ionosphere to work properly. That mean that the lower frequencies were affected first and longest.
For a direct line of sight radar system, and at frequencies above L or S band, I’d say maybe some attenuation, but not complete loss. For higher band radars, C and X band, likely a much less effect.
My big question is what was lost? The actual skin returns, or did the transponder system go out?
I think the solar activity interrupted the skin returns in where the flare effect were higher.
I spent my AF career in strat nuke ops where satcom, HF and UHF were critical. We were always alerted to the possibilities of outages from flares. Solar activity has caused localized outages in the past and this was pretty localized. Now, if it happens again in the absence of any other factors then it would be something to worry about.