"The requested page could not be found. (Code: invalid_route, controller: -, action: -)" (2.2.19 to 2.3.10)

[MattStibbs]

I am trying to upgrade my forum from 2.2.19 to 2.3.10, but every time I try and run the upgrade it returns me this error:

The requested page could not be found. (Code: invalid_route, controller: -, action: -)
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All add-ons are disabled, and the board is set to inactive. There are no obvious errors appearing in the server logs (other than this, which I think is minor based on other threads in this forum...)

I am lost as to how to debug it any further!

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