Here are the IDAT run switchover points for the first three images of >>121 >>122. They all exhibit the same pattern >>124 of ending the first IDAT run with an empty non-compressed block so that the starting deflate block of the second IDAT run is aligned on a byte boundary.
iQSyNAQ.png
0000eb10 fd 4a ae e1 45 af f4 37 7e 3f b7 80 ff 07 00 00 |.J..E..7~?......|
0000eb20 ff ff 8c e5 1b 02 00 00 40 00 49 44 41 54 ec dd |........@.IDAT..|
0000eb30 0d b4 ae db 5c 30 fc 7b 9f 73 90 c7 d7 b0 37 51 |....\0.{.s....7Q|
AJlNWhC.png
0000ddd0 2f 81 11 88 bc 00 00 00 ff ff cd 0d 8d 01 00 00 |/...............|
0000dde0 40 00 49 44 41 54 ec dd 7f d4 f7 d9 5c 2f fe 7b |@.IDAT......\/.{|
hLzyLXE.png
0000f940 87 d6 b5 de de 96 00 01 02 04 0e 43 e0 ff 00 00 |...........C....|
0000f950 00 ff ff 1a fb 96 b3 00 00 40 00 49 44 41 54 ec |.........@.IDAT.|
0000f960 dd 7f d0 b5 5f 59 10 7a 70 42 72 40 3d 88 26 86 |...._Y.zpBr@=.&.|