I am having the same issue. My vault contains ~790 entries. I have tried all the tips in this thread and found that it is certain entries in my vault that causes the export to error. I found this by copying under 200 of my entries into multiple new vaults and trying to export. I was successful in exporting from two out of the four new vaults. For the two that errored, I slowly removed entries until I was able to export successfully. I then created another vault and slowly added a handful of entries at a time, until it would error. Using this elimination method so far I have found at least one entry that is causing the export to error for whatever reason. If I have a new vault, and copy said entry to the vault by itself, the export will error. I know I have at least one other entry to find.