Question about infinite streaks

Two nights in a row I was well into an infinite streak when all of a sudden, opponents jumped back up to max level. I know I was well over the hump, so I'm wondering what I did to cause the difficulty to spike. This was in the basic arena, and once I was well into infinite, I started using some 3*s
0
Comments
For basic hero you can't use teams of 3/30 3* and for t4B never use 3* when you are on the streak
This is correct. You can use 1/10 4*'s in the Basic but I only pair them with 2 Max 3*'s to be safe.