You're appearing in searches by them, but they're not looking at your profile. It's likely that it's more important who else is coming up in their searches, or not coming up in their searches. You're making a guess, but you don't know. If they were focused on you, LinkedIn would be saying that they were looking at your profile. But even then, the question would be why was your profile interesting, which is very broad and open-ended, with few of those indicating job insecurity.
It could also be that the company is searching on people who have LinkedIn profiles that say they work for the company. I've only heard of two scenarios where companies would be doing this.
The more likely scenario in my mind is that they're receiving reports of unfavorable comments made on LinkedIn by people who claim to be their employees, and these people may not actually be their employees. They're thus needing to do damage control and disavowing these people. In this scenario, you're not involved at all.
The other scenario I know of for searching repeatedly for people who work at the company is that they're concerned about the dearth of their employees with a LinkedIn profile stating that they're working for your company. In this scenario, while you're somewhat on their minds, you're one of the good people who has done what you're supposed to do.
They could be looking for people in the local area as candidates to try to recruit due to a dearth of people with the right skills applying for any open positions they have.
The scenario that people fear is that they're searching for people with skillsets matching yours. But most people have more than one job skill that is important for their job, and each job skill they have is applicable to multiple jobs. They could be looking to hire somebody for a different job that is just in some way similar to yours.
It's also possible that they have business deals in the works that would cause a significant increase in your workload, to the point that they would need multiple people for your job. While most employers hire after the workload has been attained, it sometimes goes the other way. My first full time job was one of these, as they had a customer who wanted people to be able to be on the job on the first day of the new contract.
But rather than just trying to calm your fears, the other question is what should you do about it. You say you haven't gotten performance feedback. Have you asked for performance feedback? If not, it's probably a good idea to ask if there are things that you can improve. This is probably a good idea in general when you haven't been getting any performance feedback.
Of course, it's also possible to go overboard on it; if you are constantly asking how you can improve when your boss is satisfied with your work, it could cause the problem you are wanting to avoid. If my boss wasn't ever giving me any feedback on how I was doing, I'd be striving to keep it down to one or two requests for feedback a year, but I'd probably do more like half a dozen.
There's also your own self-assessment, and figuring out how you can work on improving the areas you see that you can improve yourself. Since you apparently have slack time occasionally, you may even be able to spend some time focusing on improvement without working on that outside of your normal work hours.
If you're unable to come up with ways to improve, either with the boss's help or on your own, one technique that I've found that can be useful is to imagine how you would teach somebody to do your job. Teaching others is often cited as one of the best ways to learn, but rarely do I see anyone explaining how that works.
When you're teaching somebody else, you have to review all of the things you know about the subject and how to convey them. You review everything at a much more careful level than you're likely to when just reflecting on how you've been doing. Thinking about how different people may react to the instruction, you can sometimes have insights that you'd not normally have.
Of course, actually having a student to teach makes that exercise much more effective, because a real other person will respond differently than your imagined other person. The real other person will not actually know some of the things that you assume everyone would know, and if they're a good student, they'll let you know that. Otherwise, if you're good at quizzing them, you'll find out that way.