As mentioned on the day of the 5yr TIPS auction, there is nothing weird here

The April 5yr TIPS almost always price at a higher yield than the October issue because CPI is seasonally higher in the summer than in the winter, and TIPS payments are based on non-adjusted CPI... https://twitter.com/JeffSnider_AIP/status/1390074667487186950

Thus, the October 2025 5yr TIPS didn't move when the April 2026 5yr TIPS was auctioned at a 20+ bps higher yield. Because this is normal and the market is pricing in seasonally lower inflation over the October-April period as expected...

Conversely, here in October 2019, the April 2024 5yr TIPS didn't move when the October 2024 5yr TIPS was auctioned at a significantly lower yield. This is also normal and reflects the market pricing in seasonally higher inflation during the April-October period...

Unfortunately, contract roll effects are common and can cause confusion if forgotten. For a semi-annual reminder on this effect specifically (and much more great Treasury market content), highly recommend following @beth_stanton, she knows what's up https://twitter.com/beth_stanton/status/1385218130688057353?s=20