.WAV files no longer readable after Yosemite update

Question

The issue:
I recently did the switch to Yosemite. I now find some .WAV files to be no longer readable through FCP X, Preview app, QT, etc. BUT, I can open them through VLC, and also Soundtrack Pro. The problem:
An FCP X project with this .WAV files has already been edited, with multiple cuts (46 to be exact) throughout the 35 minute timeline. The file is still visible on timeline with all cuts but is now silent. Looking to relink that audio with a working file. The original files' timecode starts at 09:46:30:09, with 7 channels of audio. What I tried to do:
Open in Soundtrack Pro and simply "Save as" a new .wav file. Still not readable. Then brought the original file in to a new Multitrack Project in Soundtrack Pro, exported to .wav, which is now readable by all programs, but cant be relinked since info are not matched (channel count and timecode) "Incompatible file.
The original file and new file have different audio source and channel counts.
Relinked files must have the same media type and similar audio channels as the original files, and must be long enough to cover all the clips that reference the files." 
My system:
FCPX (10.1.3)
OS X 10.10 (Yosemite) iMac (27 inch, Late 2012)
3.4 GHz Intel Core i7
32 GB 1600 MHz DDR3
NVIDIA GeForce GTX 680MX 2048 MB 

Answer 1

Thanks Martin. Thats just what I'm going to do. For the record, I have been dealing with Apple support concerning this issue for the last month. It's been a frustrating and exhaustive process and the outcomes has been underwhelming to say the least:
It seems that under OSX Yosemite, Apple Core Audio , which plays audio in all the apple apps: QT, iTunes, FCPX, Logic Pro X etc, can no longer read multi-track WAV files larger than 2GBs. I tested this extensively myself, and the support staff member I was dealing with was able to re-create the problem at his end.
Apps that do not use Core Audio CAN play the WAV files: QT7, Adobe Premiere, Audacity etc.
Using this information the support member helping me escalated the issue to the Apple developers teams for both FCPX and OSX. He said he was really unimpressed by their response, and that while they acknowledged that there 'may' be an issue with Core Audio they didn't care enough to investigate it. He said that while a fix may come in the future there is no timeline for it to happen. He said he wasn't allowed to recommend that I downgrade, but he then rather embarrassingly admitted that I have no choice if I want to have a functioning project again.
Which makes a mockery of my decision to use FCP over Premiere based on the assumption that Apple would better support their software. FCP has pretty much ****** me off right from the start with its babyish interface and glitchy behaviour. Now I have to downgrade my system to Mavericks, in order to limp to the finishing line with this edit, before I will be ridding myself of this junk for good.