Hi Eric, do you realize that WAN Accelerators process one disk at a time? Meaning, if some job is using it, other jobs will have to wait inline until that job has no pending tasks to process. Can you check to make sure this is the case?
Overall, we have not had any support cases around "unreliable" behavior of WAN Accelerator. There are some common questions are related to deployment best practices and sizing, especially on very fast WAN connections, but no real issues reported. In fact, the upcoming Patch 1 (that is meant to address all known issues reported through technical support to date) does not bring any fixes related to WAN Acceleration, so this is arguably the most stable part of this release. Moreover, we've been running WAN Acceleration jobs internally for a few months now with great success.
Of course, there is still a chance you've ran into some bug, so please open a support case so that we could investigate. The functionality is brand new, and of course the chance of it having bugs is higher than for any existing functionality. This is normal: software is written by humans, and we all make mistakes... I mean, show me at least one major vSphere or Windows release without a few critical bugs... What matters is how fast they are addressed by the vendor, and we are ready to work with you and resolve all issues in prompt manner.
Regarding your question on initial sync, it is normal for that to take a few days depending of the data size and available WAN bandwidth (this is why we recommend that you perform initial backup seeding whenever possible). However, this is not mandatory, it will work without the initial seed too. The full backup will eventually complete by transferring only deltas to already transferred data, and you do not need to do anything from your side, not even put large amounts of angry smileys and question marks in your posts
Please, be sure to open a support case - the sooner you will do this, the sooner our technical staff will be able to confirm everything is running as expected in your environment. Without seeing the debug logs, we can only be guessing.
Thanks!