First I would get the cablemodem logs to see what is happening. Your cablemodem will have a web portal to login and check logs.
I had the same issue on drastic signal loss, They charge 75$ if they come inside the house and have to fix anything. If they do any outside work, they do not.
I had a bad old line going from cable box to the cox junction box which was losing signal. The tech replaced the entire line and within a week, they came back and buried the cables under the ground.
My initial thoughts were the same as yours, but the tech was awesome, they came on time and fixed the issue in no time. You never know you might have a bad line like I did.
Hope this helps.
