Excuse me, why do beginning of spring sometimes have solar terms and sometimes not? What does beginning of spring mean?

Beginning of spring: beginning of spring is standing, and beginning of spring is beginning of spring.

Why sometimes there are solar terms in beginning of spring, and sometimes there aren't?

Simply put, the 24 solar terms are determined according to the position of the earth when it revolves around the sun, that is to say, the time span of the 24 solar terms exceeds 365 days. The average lunar year is only about 354 days, so there will be some lunar years without beginning of spring solar terms.