I've been researching cryptographic modes and came across an obscure mode called interleaved CBC (ICBC). I can't find a lot about it and am wondering if anyone knows anything more.

It's basically CBC but where instead of chaining the last block you chain the n-mth block where m is some constant. This allows some amount of parallelization. For example if m is 8 you can do 8 blocks at a time. For message indistinguishability you'd also need an IV as wide as the block cipher times m, which could probably be expanded from a shorter IV.

Anyone know what this is? I suppose it would be considered obsolete but it would perhaps have some desirable properties in certain applications.

Edit: as near as I can tell this would be identical security-wise to splitting the message into m smaller messages and encrypting each with CBC. The fact that the message is split by being "striped" rather than split into chunks seems irrelevant. Does this basically just reduce to CBC (assuming the IV is unique per stripe)?

Also this would have to be authenticated of course to prevent padding oracle attacks.

This is expected behavior since 7zip uses Cipher Block Chaining (CBC) mode for encryption. For which you need the Initialization Vector (IV) to be unique and unpredictable.
It was using 64-bit IV but fortunately, that was changed to 128;

Encryption strength for 7z archives was increased: the size of random initialization vector was increased from 64-bit to 128-bit,
and the pseudo-random number generator was improved.

If the encryption of the same file results in the same ciphertext then we will be thought that there is a problem with the IV generation. Hopefully, from here we see that there is not.
Note 1: 7zip uses $2^{19}$-times iterated SHA256 to derive the AES-256 key from passwords. This is not safe from massive parallelization. A password with high entropy like diceware is recommended.
Note 2: The first comment under question claims that CBC mode of operations has IND-CCA actually it can't, it has IND-CPA. See the seminal work of Rogaway on modes Evaluation of Some Blockcipher Modes of Operation
