NSIS is a new school just finishing its second year, there are administrative procedure problems, yes, but they are whims of the owner usually softened by the farang admin.
???Providential fund- all money put in by teachers was refunded, school matching funds were not... legal problems with set-up originally a (US) 401K type plan.
Mistreatment of staff? After what i've seen elsewhere, no... Most schools in Thailand with the exception of the big three, do not have substitutes on call and need to cover classes sometimes greatly inconveniencing others, but this is a situation you must accept in international schools in Thailand, the qualified pool is small. Other mistreatment issues are a muff, personality clashes abound in an environment where people from disparate countries come together for their own idiosyncratic reasons.

August holidays? a scheduling error, not uncommon in new schools just getting their feet under them, Will someone say they are cut short again? The school year begins a week earlier this year than last, but this is not 'cutting holidays short'

Probation- yes, again all staff, including admin are on probation again, a technicality one does not need to worry about unless one plans on sloughing off when they are 'assured' of work for another year
--Pay raises seem to have been general this year at at least inflation matching rates.
Financial dealings with the school are a but muddy as no department has a separate budget under present rules, this does cause trouble when looking to equip a classroom. Most purchases are ok'd if they are not seen as outrageously expensive for a small school.
Teachers who consistently do their job well and have all the proper qualifications are treated quite well, even the non-westerners, though i can't speak to their wages, comparable i'm sure to the cost of their education.
No one here 'fears' for their job, Hirings and firings are not personal.
There is no reason to not work here if you are qualified and intersted in education, There is no set curriculum, which upsets some, but it allows a certain freedom to others who know how to design curricula,and look forward to an opportunity to grow with a school.
I work at NSIS, but not in Admin, i am a teacher with years of experience and have learned well that in private schools in Thailand it is 'court rules' if you don't like the rules you are welcome to seek employment where the rules are more suitable to your self.
Morning hallelujah meetings (good time to zone out with a coffee) aside, this school is doing well for its size and age. New students continue to sign up and the elementary school is growing rapidly.
So, if you are interested, join us.