@andizzle

Please add a minimal self-contained reproducer.

Side note: registering interface type assigns a number -> type mapping. The decoding process must register the same types in the same order otherwise the type numbers do not match. Is you program written in such a way that the type-registering order is deterministic and repeatable? I've had a similar problem in cznic/ql#67.

I just use plain Register

That's the only option ;-) But the interesting information is if the're only a single call to Register in the whole program, or if there are more of them. In the later case, it's important to guarantee, that they always occur in the exact same order. Note that any package you import may also call Register. As long as the encoding and decoding programs are identical and the calls to Register occur only in init() functions, this should be guaranteed. Is that the case in you failing program?

@pjebs, @cznic could be right, we are not using init() to Register. The Register can occur multiple times in dynamic order in the current program. Let's investigate.

Closing. Gob is working as intended.
Our situation was caused because the second instance, after decoding the encoded gob in redis, didn't have the struct registered.

We were doing something along the lines of this: https://github.com/pjebs/GAE-Toolkit-Go/blob/master/cache/cache.go#L84
This meant the second instance didn't have the struct registered, so would call the operation manually again - but after that it will register the struct - so it would it be good from then onwards.