So, do you mean the pattern is like 00111111, where '0' means a faulty bit and '1' a working one? I was assuming it was something like 01110111...
That makes things totally different! That would be VID(6) and VID(7) signals, coming exclusively from one of the VRAM chips: UC6. The shift register could be at fault, anyway.
Once again, the highest bits of the address lines have a totally different task: first of all, they are multiplexed (as usual on dynamic RAMs) thus RA(6) and RA(7) (the outputs of UA8) will carry A6/A7 and A14/A15 from the CPU, alternatively. But they also put the values from other video related signals: VADR(0), VADR(7), ALTVID and TWOLINE. Amongh other issues, problems with this multiplexer may imply artifacts like misplaced things on screen, by factors of 8 horizontal pixels and/or one, two or 256 vertical lines. Since you didn't mention such a scrambled display (other than the jailbar pattern) I think the multiplexer is just fine.
On the other hand, the output from the shift register goes thru one of the PALs (UG6, pin 9 to 13) so we can't rule it out, either...