My response was not the correct response.
Does my answer not convey the meaning?

My answer:
Lot of people lost the chance to meet family or friends while pandemic.

Correct:
During the pandemic, lots of people lost the chance to see their family and friends.

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I can see your confusion. “While” and “during” are both used for several actions happening at the same time.

While is a conjunction, it “conjoins” (brings together) clauses and sentences.
- We waited in the care while Jack got ready
- The doorbell range while you were asleep
It can also be used to express contrast:
- Peter wanted to go to Paris while his wife Anna wanted to go to Athens.

During is a preposition, meaning it goes before (pre-) a noun or pronoun. This placement shows the relation of the noun or pronoun to ‘something else’. “During” comes after a noun phrase (like ‘he slept,’ ‘we stayed inside,’ or ‘the fire alarm went off’). It’s also used for two things happening at the same time, but cannot show contrast like “while.”
- He slept during the whole flight.
- We stayed inside during the storm.
- The fire alarm went off during the presentation.

Your answer, if using “while,” should have been “…while the pandemic was happening.” I don’t think this correct version is incorrect, and it does get the same meaning across, since it’s not showing contrast. “During the pandemic,…” doesn’t sound more or less natural to me.

Maybe your test was online and only had one programmed answer. Or if it was given by a person going off a book, maybe your test proctor was inflexible. Either way, it seems like they wanted you to use the preposition “during,” even if the conjunction “while” could have worked. Like putting a rectangular peg in a square hole.