Some of you guys prob knew but for the benefit of the rest, these server errors can be avoided if you ensure your inventory does not have any runes/shards/souls that is close to completing a stack of 99.

For example, you have 96 souls and the LOL battle is going to reward you with 5 souls, you will get this error instead.

So especially for 3* shards from LOL which can reward up to 20+ in a battle, I'll ensure that my stacks are well below 70...