The USCIS Form I-601A is used to apply for a provisional unlawful presence waiver. Immigration waivers are used in cases where someone is inadmissible, meaning that they are ineligible for a visa or for a green card. The I-601A is special because it is only used for one specific ground of inadmissibility: those people who have spent time unlawfully in the US and who intend to leave to attend an interview at an embassy or consulate. It cannot include other waiver reasons. Those applying for a waiver abroad often use a similar but different form, the I-601.
Processing times for I-601A waivers are not standardized, but many cases are approved between 8-10 months. Sometimes a delay means that a case is going to be issued a “Request for Evidence” or RFE. Those requests typically are used to ask for more evidence of “extreme hardship.” But every case is different, and there is no way to figure out why a particular case is delayed. You can, however, submit a case inquiry once a case is outside of normal processing times.
USCIS does offer information about case processing times, but those numbers tend to be unreliable for a variety of reasons. They may offer a general picture of average processing times. USCIS processing times can be reviewed at https://egov.uscis.gov/processing-times/