What should I do if my visa application status is pending document check for an extended period?

Those status messages doesn’t tell you anything useable about when you get your application approved/rejected, and they can move both ways.

You have to read the Embassy website thoroughly and take into account the right now is high season for visa applications.

Most Embassy website gives a very thorough information about processing time.

Additional Documents reset the time counting back to 0, at the day the documents are submitted, so you should count from oct 22 ( and not oct 17 )

Some Embassies process according to travel date ( to the bennefit of the applicant) rathed than application date.

You just have to wait patiently.

Leaving the country where the application was made, is reason to be rejected, and thereby loose the 10.000 Baht visafee.

no need to do anything. Nothing you do will expedite visa processing.