Best person to answer the question is OP's own solicitor.
There are a number of situations that arise that mean that the lodging solicitor can't use what is called the Form 3 procedure- this is where the solicitor certifies the title to the PRAI and registration usually only takes a few weeks/months.
In some cases, the solicitor will have to use the Form 1 procedure- this is where the PRAI investigate the title. I have some Form 1 dealings languishing in the PRAI since 2015. They have a chronic shortage of experienced Title Examiners.
Most solicitors would advise a purchaser if they anticipated a long delay in registration.
mf