The cable strain relief has pulled out from your wall due to horizontal wind force deflecting your Service Entrance cable.
Apparently the strain relief bolt stripped and the nut and washer fell down inside your attic.
If this is not fixed your SE cable will have a short life. Copper cannot stand much tension
so the steel messenger cable that fastens to this anchor
carries the bulk of the tensile force.
If your AHJ permits it, get a heftier strain relief from an electrical supply house and have it fastened properly on a non-rainy day by someone who knows what they are doing
who is not afraid of insulated wires carrying 240V while working on a ladder.
If the strain relief bolt is not stripped
you can get a 1" long stainless steel or galvanized bolt connector that has female threads inside
and use this to couple the strain relief bolt to another bolt fed from the inside of your house.
That way you don't have to mess with the messenger cable.
There should be some sag in the cable when you're done. Look at other undamaged houses to see how much sag in how much distance the electricians have put in these cables.
I've re-anchored the strain relief bracket on my 50 YO house with two lag screws; it was starting to pull off and fortunately I noticed it while pulling ivy off the walls.