Emergency-Injury-793's journey

I recently received a verbal offer for a graduate job, which I was really excited about. About a week and a half ago, I got the call confirming the offer, and the next day, I was asked to complete a pre-employment check. I promptly submitted all the required documents and provided two referees as requested. However, it's been quite frustrating since then. I still haven't received any conditional offer letter detailing the contract specifics like my start date and salary. I reached out to HR for an update on Tuesday, and they informed me that they were sending out the reference requests that day, but the conditional offer letter was delayed due to an IT issue. I followed up with my referees, and they confirmed they had already completed the reference questionnaire. I sent another email to HR yesterday, but I haven't heard back yet. To complicate things, the hiring manager is currently on holiday, which leaves me feeling uncertain about the whole situation. I'm wondering if this lack of communication is typical after a reference check and whether I should be concerned. Do they usually need approval from the hiring manager before sending out the conditional offer letter? Any insights would be appreciated.