[Nook HD, HD+ Android Development] amaces:
Bug Reports Enabled

For the more exotic bugs that are not yet described in Hashcode's CM12.0 Bug Reports, feel free to leave feedback here.

The MD5 hash for cm-12.1-20150622-UNOFFICIAL-ovation.zip is 3fff2e031c6c6daa5c6eb1ad2b9e78ed; I have the exact same build running on my device. Now, since you have an older backup, can you do a little experiment? Wipe data, cache, etc, plus system, flash everything that you need, then restore your backup, but only the data partition (that's the only partition worth backing up anyway). Let the system/ART do its thing, then report back.

If you have a backup for /data, you could attempt what I wrote above, should this happen again.

No need to be sorry… I mean, I try to fix things, but it's not like I'm proselytizing my builds or anything ;) Since I have almost zero experience with TB, and haven't used it in years, let's hope that someone else can provide a solution. The Wi-FI issue is a lot more problematic; I assume that you checked the advanced options in detail, right? And you mean reconnect after sleep, or under other circumstances? You have to be aware that your Wi-Fi AP configuration could also be responsible. The wireless drivers haven't changed much while porting to CM12, certainly not as much as other parts of the system, and we're still using the same TI supplicant. At any rate, feel free to open a Bug Report and post more information about this issue (ideally, logcat and dmesg output, although it's probably too late for that if you already switched to CM11).

Probably close to zero… F2FS support is not only about kernel support, but also about ancillary userland tools, and more important, the UI hooks, which TWRP exposes automatically. I don't know about the state of the CM recovery these days, but if its UI doesn't support F2FS already, it'd require significant work to add it.

Now, the part about TWRP not flashing CM images reliably is simply wrong; it may have its exotic bugs, but not with installing ROMs. If you look inside one of those ZIPs, you'll see that much of flashing logic is implemented in custom scripts, and the final operations are mostly writing images to the proper partitions, maybe restoring a few files with backup support. These operations run similarly on any modern recovery, which is simply a highly customized embedded Linux/Android distribution.

Empirically, I must've flashed hundreds of images on just this one device since January, and have used TWRP probably close to two years, after another couple of years of CWM-type recoveries. It's possible that earlier TWRP versions (< 2.8.4) had issues (with CM12's custom scripts), but I jumped from 2.7.x to 2.8.5, and never had issues with basic ZIP flashing on any current version… minor annoyances with wrong timezone, touchscreen responsiveness, etc, yes, but not with the main functions that make a recovery.

Yup, no major changes to kernel since the end of May :( Buffer underflows will remain whenever you have more than four HW accelerated overlays (at least on ovation). Hacker's Keyboard uses pre-KitKat code, and should be fine; I've been using it without issue for the past month or so.