I did the back-to-back tourist visa thing for a few years, before covid. I never had any problems. Twice immigration pulled me aside talked to me a bit and let me in. Each time the IO would say 'next time you come....'. They knew I intended to stay long time.
One of the conversations with the IO, he told me its best to go to other countries for a couple of weeks each visa run.
Based on my experience I think you will be ok. However, I recommend travel with a plan b. Cross at land borders so when they deny you, you can easily travel to the next border and try again, or know you may get rejected and plan for unintended trip to SG.
I found Australia a pleasant place to spend a few weeks. A couple of the embassies there will give Americans Multiple Entry Tourist Visa. These may no longer be available.
I usually get a window seat so 1.7 second guy is never me. However, I much prefer 1.7 second guy over the guy that goes through the metal detector 5 times because they just can't figure out - take of all of your Jewry
Pre Covid there was a limit of 2 land border crossings per year, I think. Unlimited crossing by air. I did back-to-back extensions for years (2 or 3). Advice given to me by an immigration officer is to stay in the other country for a couple of weeks. So at the time I would go wherever spend a few weeks and come back with a fresh new visa, I never had problems.
I have heard of people getting denied entry so it is best to have a plan B.
I have inquired at the hospital a couple of times about donating blood. Each time they tell me come back in a few months when they're doing a blood drive.