How can I avoid losing my items in the first place
One current workaround to this problem is to only store Soul Shards in your main backpack, not your other bags. The bug will not manifest itself if you follow this rule. Another suggestion would be to ensure that you are always playing with a lot of empty inventory space.
If any more workarounds to the problem are discovered, I will update this post.
I hope this clears up some of the confusion. Thank you for your patience while we get this issue resolved.
Edit: A better workaround to this problem is to actually not store any Soul Shards in your main backpack at all. Instead, store all of your Soul Shards in your other bags, and this problem will not occur.