What does MS Word add-in error code "0x-2147208704" mean?

Occasionally when I launch my add-in in MS Word on Mac (Word version 15.34), my add-in crashes after I make several mouse movements within the task pane itself (sometimes just happens when hovering, scrolling, or sometimes after a click).

I found this page which lists a directory where logs are stored (~/Library/Containers/com.microsoft.Word/Data/Library/Caches/Microsoft/uls/com.microsoft.Word/).

Upon examing the log file I found 30 of the same line (pasted below). What does "ErrorCode": 0x-2147208704 mean and how can I fix this? This crashing seems to only happen in Word for Mac and specifically only on my machine (others I've asked cannot reproduce it).

10/19/2018 03:48:53.280   com.microsoft.Word  0x70000fd0b000                          com.microsoft.Word  ODP Sandbox API ayc91 Error   Error in API pipeline: Failed to execute api. {"Api": 0x00000068, "ErrorCode": 0x-2147208704, "AppId": "wa104381028", "AssetId": null, "StoreType": 0x00000000, "DocCookie": 140616520894464, "InstanceId": "{44AD1334-2A8E-AD46-B1BA-8095B4C1E2C7}"} 43BAFD84-BBDA-4BCF-A3F9-3B984F2D6C13 

Updating Word to version 16.16.3 fixed this. Thanks @RichMichaels!