Mind spike, a 2nd-level spell included in Xanathar's Guide to Everything (p. 162), seems to use different damage dice for the base damage and for additional damage when cast at higher levels.
I have the First Printing of XGtE, which has the following text (bold for emphasis mine):
You reach into the mind of one creature you can see within range. The target must make a Wisdom saving throw, taking 3d8 psychic damage on a failed save, or half as much damage on a successful one.
At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d6 for each slot level above 2nd.
I have not been able to find any other spells that use different damage dice sizes (d4, d6, d8, etc.) for the damage at the base level and the "At Higher Levels". (The only quasi-exception are spells like ice storm that that use multiple different damage dice at the base level for different damage types, but in this case the damage at higher levels uses the same die size as the matching type of damage at the base level.) So my suspicion is that this should do base damage of 3d6 or additional damage of 1d8 for each slot level above 2nd.
Has the mind spike spell's damage been errata-ed, corrected in later printings, or is there any other evidence that this is a misprint?