I think it is just slack wiring. DS18B20s run on practically nothing and, if adding a fifth to a group of four was the straw that broke the camel's back, I'm sure we would all know about it.
I've wired it up 3 or 4 different ways on two different breadboards. Same result. Any 4 sensors works fine. Add any 5th sensor and they all disappear.
I rather suspect something else is going on. Reducing the pullup is common practice when using long cable runs to the sensor, which is probably not the case here, and even in that situation, 2.2k is about as low as I have ever heard of.
I can't comment other than that I hope you aren't using the parasitic power mode. I only use four at a time myself, all waterproof 3m, but there have been instances on this forum of people using more, and with no problem. Using waterproof sensors with cabling means you have gotten round one DS18B20 problem - using cheapskate cabling. The type of sensor per se is irrelevant, and the only issue that might come up with Arduino is whether it is 5v or 3.3v, which is not relevant here. I believe the sensor only uses the pullup when it is actually passing data, which rather suggests that the number of sensors has no bearing on the size of the pullup. I think this is one for el Supremo, who is rather supreme on these matters..