Apart from explaining the problem to the engineer, is there anything else I should ask him to check/carry out?
The engineer should be carrying out an end to end PQ test, look over their shoulder as the test runs, look for red crosses or grey exclamation marks rather than green ticks, ask the engineer to explain the results.
Ask them to run a manual sync test, noting the sync rate, snr, and theoretical max sync. Ask them to rerun this test on the incoming pair (where the line enters the premises. Ask them to check that with the SSFP removed
all other extension points carry no dial tone.
If the sync rate doesn't vary between the two test points, ask that they ring the FTTC SMC and request a recalc of sync rate, this should be done upon completion, or if the capped sync requires removing to continue faulting.
Good luck.
Where are you in the country ? It might be me !