Media Offline Problem

I'm having an offline media problem in Davinci Resolve. The project I am editing uses footage from two different cameras, an A7S III and an A7S II, stored in adjacent files in a project folder on an external hard drive. The filepaths have not changed, and the hard drive on which the raw media lives has not been disconnected. The footage displayed properly when I created the project; I used Davinci to transcode, and was editing happily on my proxies when I attempted an export and discovered the footage from the A7S III had gone offline. I sense it is a codec issue, but I'm not sure how exactly. Somehow, the program has decided not to display this subset of camera originals.

Now, when I go to relink the media, I go to the file location, and the file is grayed out and is not selectable (why?). These are regular camera media .mp4 files. To make matters more confusing, the footage from the A7S II is fine, but the footage from the other is not.

If it helps to know, they are slightly different codecs - and quicktime will not play the ones that are offline, but will play the ones that are. But VLC plays both, so I know the media is not corrupted.

I tried relinking the file but can't select the media (I also can't select the media for the subset of footage that does play, oddly).

I am editing on a 15" MacBook Pro 2015, running Monterey 12.5.1. The project was created on Davinci 18.1, and I updated to 18.1.4 Build 9 in an attempt to fix, but it hasn't worked.

The footage that does not play has these settings:
83.2 Mb/s, 1920*1080 (16:9), at 23.976 (24000/1001) FPS, AVC (Component) (High 4:2:2 Intra@L4.1), Overall bit rate mode: Variable, Overal bit rate: 88.1 Mb/s

The footage that plays has these settings:
47.6 Mb/s, 1920*1080 (16:9), at 23.976 (24000/1001) FPS, AVC (NTSC) (High@L4.1) (CABAC / 2 Ref Frames)
Overall bit rate mode: Variable, Overal bit rate: 49.4 Mb/s

I'm realizing my OS may not be compatible with this specific sony codec... Looks like my options are to update my computer (I have the most recent OS a mid 2015 MBP can load), or batch convert all of my footage to Apple Pro Res 422 - if I've already done some grading, will that look different? And wouldn't I need to manually replace every video file one by one?

I'm still confused why Davinci crapped out on this codec mid-project when I didn't make an changes to my OS...

Would switching NLE's be an option? Not if I still want to grade in Davinci, right?

I'm realizing my OS may not be compatible with this specific sony codec... Looks like my options are to update my computer (I have the most recent OS a mid 2015 MBP can load), or batch convert all of my footage to Apple Pro Res 422 - if I've already done some grading, will that look different? And wouldn't I need to manually replace every video file one by one?

Is this Resolve Studio or the free version?

Generally speaking, whenever anybody starts to edit anything in an H.264/H.265 codec, my advice is to transcode everything straight across to ProRes 422 (or 422HQ if you think it makes a difference), same res, no color correction. Then consider the ProRes the "new" masters and just archive the original H.264 files.

Using an 8-year-old computer to try to use 2023 software is a challenge. What specific OS are you using? There are some limitations with Catalina, but that may only apply to 10-bit codecs. If the cameras are 8-bit, it should work fine. (Not 100% sure about this.)

The real problem with making the switch at this point is getting the existing timelines to relink. This is all part of workflow, and getting the workflow right is one of those things you have to do at the very beginning. Changing horses in mid-stream is tricky and may require some manual work to fix it all.

I'm using Monterey 12.5.1.

My proxies are 422 so it's not a major hassle to just use those as my raws, I'll just have to reconnect every clip I end up using in my cut. Not ideal, but it'll do for now.

Can the new Mac OS handle Sony codec raws? I've been considering upgrading for a while but have been holding off for a number of reasons - I edited a project in Premiere on a new 2021 M1 Mini this winter and found it surprisingly bad at handling 10 bit footage as well, though shot on a Panasonic.

But if making working in ProRes everything is they key to unlocking compatibility, maybe that's just my life now?