Vibrations from handlebars are well known to cause accuracy issues with wrist based HR while riding outside. (OK for indoor riding though).
And Whoop 3.0 is just a “dumpster fire” in terms of accuracy. Whoop 3.0 Band & Platform In-Depth Review | DC Rainmaker
Not sure yet whether 4.0 is any better.
Regular washing of a chest strap, or just replacing the fabric part (keep the sensor unit) can help address the accumulation of salts from sweat that can cause issues with chest straps.