Here's PC's animation scripts:
0:
00 FE C0
1:
C7(0001, 01) 01 F6 E5 EE
2:
C7(0001, 02) E5 EE
3:
C7(0001, 03) 02 03 04 F7(03) 05 E5 EE
4:
E8 C7(0001, 04) EA 06 07 08 EC 09 E5 EE
5:
E8 C7(0001, 05) EA 0A 0B 0C EC 0D E5 EE
6:
E8 C7(0001, 06) EA 0A 0B 0C EC 0D E5 EE
7:
C7(0001, 07) 0E 0F AD(0E, 044C, 05, 0A) AD(0D, 044C, 05, 0A) D8(05, 0010) F7(0C) 10 11 E5 EE
8:
E8 C7(0001, 08) FC EA 12 13 14 EC 15 E5 EE
9:
C7(0001, 09) 16 EE
10:
18 FE C0
11:
C7(0001, 0B) 19 F6 E5 EE
12:
E8 C7(0001, 0C) EA 1A 1B 1C EC 1D E5 EE
13:
C7(0001, 0D) 1E EE
14:
C7(0001, 0E) 1F EE
19:
C7(0001, 13) C3 F4(0F) F3 B8 EE
Note that the majority of these start with C7(0001, XX) as the first or second command. This code tells the animation engine to make the actor in enemy slot 1 (or one slot ahead of it, I'm not sure) perform animation XX. That's how it communicates with Jamar Armor to make it move along with PC. So when one of the PCs is moving, it's essentially telling the next one to perform its animation too (it looks like you have more than two PCs in that video). If Harpy is farther down the formation list there, it will try to make Harpy perform some of these animations too. However:
0:
A9 C9 00 C1
1:
01 F6 E5 EE
2:
E5 EE
3:
BE(21) BE(26) C2(26) FC 02 D1(04B0, 0000, 08) F0 03 04 FA F0 05 E5 EE
4:
E8 B6(00) AA FC EA 06 C9 07 CA 08 EC 09 E5 EE
5:
E8 B6(00) AA FC EA 0A C9 0B CA 0C EC 0D E5 EE
6:
E8 B6(00) AA FC EA 0E C9 0F CA 10 EC 11 E5 EE
Harpy's only got 7 animations. Trying to execute animation 8 or higher will likely cause an error. I'm not sure how the game handles this, but that's your explanation of what's going on.