Hi, this issue still occurs regularly for us, so I've spent some more time investigating it. I believe it boils down to the following discrepancy:
a) In the type registry, it is perfectly fine to define multiple types with the same name, they each get different type ids. For a given storage item, the type registry identifies the type of the storage item via this unique type id.
BUT
b) The rpc-core package identifies the type of a storage item via its name, (literally a string). Because of the way the internal lookup into the type registry works, if multiple types with the same name exist, the last one (with the largest type id) is used, which ultimately causes the above error.

I think that somewhere in this function https://github.com/polkadot-js/api/blob/a15d0dd0df6b0ba87d88eb7f637b9e1d6e0fb87a/packages/rpc-core/src/bundle.ts#L499
it should be possible to define the type used for registry.createTypeUnsafe() via the type id (integer) instead of the type name (string).

Hi, this issue still occurs regularly for us, so I've spent some more time investigating it. I believe it boils down to the following discrepancy: a) In the type registry, it is perfectly fine to define multiple types with the same name, they each get different type ids. For a given storage item, the type registry identifies the type of the storage item via this unique type id. BUT b) The rpc-core package identifies the type of a storage item via its name, (literally a string). Because of the way the internal lookup into the type registry works, if multiple types with the same name exist, the last one (with the largest type id) is used, which ultimately causes the above error.

I think that somewhere in this function https://github.com/polkadot-js/api/blob/a15d0dd0df6b0ba87d88eb7f637b9e1d6e0fb87a/packages/rpc-core/src/bundle.ts#L499 it should be possible to define the type used for registry.createTypeUnsafe() via the type id (integer) instead of the type name (string).

Thanks for doing the initial research, I am looking into this as we speak!

@TarikGul here is some (possibly) relevant context - there was a similar issue with scale-typegen:

paritytech/scale-typegen#14

For your information, it is possible to hack this to work, by not relying on the outputTypeName to be unique and instead constructing the lookup name.

in polkadot/rpc-core/bundle.js you could modify "_newType" like this

    _newType(registry, blockHash, key, input, isEmpty, entryIndex = -1) {
        const pallet = registry.metadata.pallets.find((e) => e.name.toString().toLowerCase() === key.section.toString().toLowerCase());
        const call = pallet?.storage.unwrap().items.find((e) => e.name.toString().toLowerCase() === key.method.toString().toLowerCase());
        const typeid = call?.type['value']['value'].toHuman();
        const type = typeid ? "Lookup" + typeid : "Raw";
        const meta = key.meta || EMPTY_META;
...

Essentially i lookup the typeid of the output value of the method in the registry and then use that instead of the name. It works for me, but obviously you could make this more elegant.