This is not bizarre, it's a reflection of how the IMO is scored: 6 questions with scores from 0-7 but partial credit is rare. It's really a score of 5/6.
The top of the table is full of 7 and the bottom is full of 0, but in the middle there are a lot of intermediate points. It's not uncommon "7 ? 0 7 ? 0" because the 1st and 4th are usually the easiest and the 3rd and 6th the hardest. But there are a of of other combinations due to stupid mistakes and lucky solutions and different personal styles/preferences that make some problems easier/harder for each contestant.
You're right, it's less uncommon than I recalled, and thanks for the source. But I don't think that 35/42 is suspicious/bizarre, and it does look like the 5x7 scores make up the bulk of the 35s.
It's not rare at all. I can't find the 2026 results, but here are the 2025 ones.
https://www.imo-official.org/results/individual/year/2025/
The top of the table is full of 7 and the bottom is full of 0, but in the middle there are a lot of intermediate points. It's not uncommon "7 ? 0 7 ? 0" because the 1st and 4th are usually the easiest and the 3rd and 6th the hardest. But there are a of of other combinations due to stupid mistakes and lucky solutions and different personal styles/preferences that make some problems easier/harder for each contestant.