I've gone through number ports in the US three times (seven if you count each number separately) without a single problem. Each was completed within several hours, and dual service time was somewhere between minimal and non-existent (suddenly the old phone stopped and the new phone started). This is in line with what I've heard from friends and relatives, too.
I've read some porting horror stories online over the years. Yours is probably something like the 6th or 7th. I assume things do sometimes break, but it doesn't seem to be particularly frequent, considering millions of people switch carriers every year.
It breaks surprisingly commonly. You've moved 3-7 times in a few years. I move different customers numbers at many times a month. Around 20% of the time we have issues with fail to fast busy for 8 to 12 hours where no system on the telco side takes a call.
I will say this though, switching mobile goes rather well almost all of the time. Porting numbers on fixed telephone lines is much more apt to fail.
I've read some porting horror stories online over the years. Yours is probably something like the 6th or 7th. I assume things do sometimes break, but it doesn't seem to be particularly frequent, considering millions of people switch carriers every year.