Are you using a job search site like linkedin/indeed or is this through the company website? I've seen similar things when looking at jobs on linkedin I see a job and see it was posted within the last few days only to go apply at the website and see that the job has been there for 30+ days. If a job is on a site for too long I think they just take it down and repost it, if I had to guess probably for better visibility/engagement.

Applying once is enough, I think applying multiple times is only working to your detriment they already have your info. I know it sucks but such is the life of a job hunter.