About Microvalues: In the Savings Budget I scanned through columns M, P, T, X, AE, AF, AG, AH, AJ, and AK for my Nov 2019 an Sep 2020 budgets. The only place these microvalues appear is in AJ and AK. In Nov 2019 I have 2 affected categories, and in Sep 2020 I have 13.
I originally thought this had something to do with adjustments but in my 13 there’s at least 1 that has never had an adjustment. There are multiple that have only an adjustment from my initial Nov 2019 budget but aren’t affected in that period. 
It’s weird.
I made a conditional format for all of the Rollover Mods rows in my Envelope sheet that highlighted non-zero values. I checked everything that highlighted and there was only one microvalue here. I did a quick scan of some Rollover and Actual lines and found quite a few. I chose 3 categories and went through manually correcting them. After I ran Analyze Budgets History they came right back so I think the source of the problem is likely in that function. At some point, I may correct the entire sheet, then run the migration to the Savings Budget without running Analyze Budgets History and see if that keeps them from carrying over to the Savings Budget but that sounds kinda terrible. 
I was hoping to use the migration tool to keep my Transactions synced between my regular Envelope Budget and my test Savings Budget but it doesn’t seem to be working out. I know this is an “off label” use but I’m hoping I can figure out what’s going wrong. When I run the migration, it seems like it’s working and at the end it’ll say XX transactions migrated, but what I find is that new transactions are excluded and then transactions from an account that I have to enter manually are duplicated. I can run it twice in a row and that XX number will be different.
Today I went through the migration process again with a clean sheet.
The “Hide From Reports” flag is not transferring to the “Categories Migrator” sheet.
At first glance most of the “Available” values in my most recent month match between the two budgets. I figure this is a pretty good way to check for accuracy. I did notice a few that were wrong. I’m pretty sure the source of the discrepancy is that some of my manual transactions didn’t transfer over. I’m also pretty sure that this is because of errors I made early on by not using the Manual Transaction tool, some combination of initially not knowing it existed and later sometimes thinking it was easier to just copy an existing similar transaction and making the necessary changes. This was before I know about the hidden transaction id column. 
Overall I think this is working really well!
Will we be seeing the “categorize transactions,” “expense budget doesn’t match income budget,” and “net transfers” warnings implemented? Those are all very useful.
Update: The budget for the last category in the Categories list isn’t being recognized, so whatever that category happens to be goes negative by the Actual every month.
Related issue: The category that was originally my last never shows the Actual, even though it’s clearly deducting it because the Available continues to decrease. When I moved a different category to the last, the original continued to behave this way while the “new last” was affected by the issue, it had all of its Actuals properly displayed. Also when that original category was no longer last, and continued to not show it’s Actual, the “Available” always remained the budgeted amount, but didn’t carry over to the next month, so for example each month it would say: Savings: $0, Budget: $9, Actual: (blank), Available: $9. It’s not carrying over the Available to the next period so it’s seeing that it was spent, but the display is not reflecting it. It does show in column P.
Update to the update: I feel like there are gremlins in the machine. I’m positive the above behavior was happening, I saw it, changed the categories, reproduced it… this morning when I reloaded my sheet it wasn’t happening anymore.
Not-really-related issue: I feel like E6 should be “Actual” and not “Actuals” to match style with the other headings.
I tried the Merge Categories on a slightly complex case and it had a minor failure:
When it wrote the budget values in the Categories sheet, it put an apostrophe in front of it. This caused the value to show up in the Budget column on the Savings Budget sheet, but it could not accumulate Savings.
Update: I went a little merge crazy in my sheet. In some cases these merges were simply category renames, another fun benefit of this new functionality. I didn’t see the “apostrophe” issue again (gremlins) but I did repeatedly see another issue. When it was writing out the new budget values in the Categories sheet, if the cell had a number it worked fine, but if the cell was blank it would write “n/a”.