Your 401k plan should outline how quickly contributions are made after payday (3 days where I worked).

If your contribution isn’t transferred to the 401 company by the payroll system on a timely basis and you lost earning opportunity the company is required to make you whole on an plan year (Jan or July) basis when they reconcile the plan (including any match that was delayed). If they don’t do this and the plan is audited they will be fined a considerable amount and will also be required to make you whole.

In a prior life I spent months reconciling a plan with a very nice and savvy IRS agent. Luckily we had very few issues - the one you described is not uncommon.

Sometimes it’s a routing error on the 401k side. Sometimes it’s an issue with the payroll software and invisible to HR. Best to start with a call to the 401k provider if HR isn’t being helpful or isn’t technical enough to answer questions. Once the 401k company provides your contribution dates and amounts, reconcile with your pay stubs (and the amounts direct deposited to your bank account since sometimes the payroll system kicks the 401k funds to your bank account when the transfer can’t be made and that may not be on your paystub). Then go to HR or Accounting if they handle payroll since it’s likely a payroll processing error. They will want to know.