I am planning on buying a new lipo pack and had a few questions.
I have seen some packs that are 2S1P. I heard that these 2S1P batteries are not as reliable as normal 2S batteries. Is this true? Should I just buy some other battery?

Wow, where does misinformation lioke that come from?

A 2S and a 2S1P lipo are the exact same thing. We've gotten lazy as lipo tech as gotten pretty mainstream and just fail to write the 1P all the time. A 2S and a 2S1P is still a 2 lipo cell battery, either designation specifies the same battery.

Ok. Thanks! I was reading that information of a Chinese website and I thought it might be true!

I believe what it should have said is that 2s2p batteries are not as reliable as 2s1p, or in today's terms, 2s.

Not long ago the higher capacity cells were more expensive, so a 5000mah pack from a cheaper manufacturer could have been a 2s2p made with 2500mah cells. 2 in series for 7.4V, and 2 parallel for the total 5000mah with 4 cells actually in the pack. With parallel cells built into a pack where they cannot be balanced individually, there is more of a chance that if you have a weak cell it could cause problems.