Today I finally figured out why,: it's because of the China's Two Sessions.

Two independent clauses: need a colon.

Several VPNs suddenly don't work today, and it seems like the Great Fire Wall wereis getting higher again, which often means something big is happening in China.

Is getting higher right now: if it was in past tense, it would be "was getting"

Sure enough, we are having sessions again.

ALWAYS need a pronoun before a verb, and you need a helping verb

These sessions will run from March 4 to March 11, so it's no wonder these classes run in such a strange way.

Need "these" for clarification.

I don't like the learning content in my major, s. Some of them weare very superficial, and some of the teachers weare not very good academically.

Need a new sentence. Since you're talking about a current thing, use "are" instead of "were".

But before the final exam, these teachers would give us the key points of the exam.

No reason to have "but": not a conflicting statement.

It's easy to pass the final exam by taking one day to recite these exam content.

You need "the" instead of "these"

But what canwill students learn?

"will" shows exactly what you're talking about.

Facing the offline classes next week, I was also worried about the school lockdown due to the epidemic, which we had experienced last semester.

No reason for "the" or "had".

In fact, I cadon't understand the need for this lockdown.

You could understand the need, you have the ability, but you don't because you disagree with it. Can=capability, don't=agreement

The city wherein which the school is located has only confirmed about 70 cases in total and now there are no more suspected cases.

use "in which" to indicate a specific place after a subject.