Why does car insurance renewal vary so much

Sheriff23

My car insurance is due for renewal on 23 April 2023.  I entered my renewal details on the MSE Compare+ calculator on 15 March and received a best quote of £245.76 to renew with LV (who happen to be my current insurer, this compares with £231.30 last year) which seemed a reasonable 6% increase.  Unfortunately I was a little to early and had to "pretend" that my renewal date was 16 April as that was the furthest the quotes went.  Today (24th March) I received my formal renewal quotation from LV at £309.64 (a 33% increase over last year). Surprised at the change in just 9 days I returned to MSE Compare+ for a fresh quote this time with the correct renewal date.  To my astonishment LV were now far from the best returning a quote of £367.39 (now 58% more than last year and 49% more than they quoted via the same site 9 days ago)!!   What is going on, how can the quotes change so much across a period of just 9 days?
Have others experienced such massive short term swings.
I will now wait for Martins optimum renewal date (1st April) and see what magical figure LV come up with!!