Hi all, first time poster. Everything I know has been self taught through trial and error and it's often been painful. . . now is another one of those times so any and all input is extremely appreciated! I'm using a

carbide 1/8" 2FL flat uncoated center-cutting end mill (largest my spindle allows NRR-2651) The end mill is 1.5" long overall.
25k RPM
Feed: 20.613 ipm
Plunge: 8.3 ipm
.01 inches stepdown
20% stepover

Whether I speed up the rpm and feed/speed and make the cut more shallow, or slow down for more strength, I seem to be getting this same result. While the end mill is cutting normally (not plunging), it begins to bite in and corkscrew down. Fortunately, I was by the mill and heard something going wrong and hit the stop button fast before I broke another tool. You can see how shallow the cuts are and this was rounding the corner during the second pass (it starts at the middle top of the block) that it decided to dig in and start cutting downward.