Hi Chris,
There are MANY, MANY reasons why a company is halted but is usually centered in two buckets:
It could be for technical reasons - if a share price jumps or falls too quickly - it could trigger an automatic halt. These are safeguards put in place by the exchange to prevent manipulation - sometimes it helps - other times it doesn't. Case in point, GME in the U.S. was halted 3 times on Friday because of crazy volume action. It still jumped each time it unhalted.
It could be also be for impending news - either the company can request or the exchange can trigger a halt based on the details of the news. It could be for a transformational acquisition, new share offering, material update to earnings, etc. There are many, many reasons why but usually is done when it is something material to the stock.
When it is unhalted, the price action varies. It can jump, fall or do nothing - it is all dependent on the materiality of the halt.
If you want, let me know what stock and I can tell you why it was halted.
Mat