Custom shutdown animation first post here...

So I'm attempting to utilize a custom shutdown animation on my LG K7 that I use for dev purposes..

Ive made backups of the original shutdownanimation.zip, and using custom pictures (same .png format, resolution,color depth, etc) I've replaced the original picture files within the zip with the new ones.  

Shutdown only displays a black screen.

So I push backup back to phone, displays LG logo again.

Deciding to experiment, I took my stock bootanimation.zip, renamed it to shutdownanimation.zip and overwrote the shutdownanimation.zip on my phone.  

As expected, this gave me the stock boot up animation during shut down.

So I decided I would take a copy of the original shutdownanimation.zip file, and simply edit the existing pictures within it using an image editor.  I just opened each of the two original picture files within the zip and used a drawing tool to write 'custom' over the lg logo, then overwrote the new picture files back into shutdowanimation.zip and pushed to phone.

I though for sure I would see the altered LG logo, but instead I got a black screen.  

Any ideas?

Update: Im wondering if some mechanism is in place to prevent alteration of the bootanimation or shutdown animation?  At first I was thinking it was some file format issue, so I took picture #150 from part0 in bootanimation.zip and replaced every odd picture with picture #150... i.e. part0 pic # 101,103,105... = pic #150 So that this way I didn't even alter any images.  Upon moving to phone and rebooting, the boot animation ignores part0 completely where I made the changes and only plays part1.
ANSWER:

So this took me some troubleshooting to fix.

During this process I was using the Linux Archive Manager GUI to work with my animation files.  This was my mistake.

At one point, as a test, I deleted folder part0 from the archive, and then added it right back in and pushed it back to the phone.

Black screen.  This was my "A-Ha!" moment.

My archive manager was automatically compressing everything I added to it.  Thus, after adding part0 back into the archive I noticed the compression ratio changed from 0.99 to 1.34...

Easy fix:  I created an uncompressed new bootanimation.zip file 

zip -r -0 bootanimation.zip part0 part1 desc.txt

worked flawlessly. Custom animations now work.