Quite a few things to consider on this one.

Are LED lights the same quality all the time.  I would say not and a faulty batch is more possible now than lets say 10 years ago.  Eg Osram/Sylvania are now Chinees brands and not made to the same high quality as before.  However most people remember them as very good brands and continue to purchase them.  The internet is full annedotal evidence of LEDs in homes and outside homes failling.  Some fail in strange ways like a PIR flood light that stays on or even start to flash.

Might be worth getting the customer to speak to the local neigbours to see if they are experiencing some thing similar?

Is there SPD type 2 and 3 at the property?  Could it be fitted?

Hire or purchase a PEL (power energy logger) from Chanvin Arnoux and leave a the property for a week or 2.  CEF and others hire them out quite cheep.

Has an EICR been done at the property recently?

How old is the current install of electrics at the house?

Quite a few things to consider on this one.

Are LED lights the same quality all the time.  I would say not and a faulty batch is more possible now than lets say 10 years ago.  Eg Osram/Sylvania are now Chinees brands and not made to the same high quality as before.  However most people remember them as very good brands and continue to purchase them.  The internet is full annedotal evidence of LEDs in homes and outside homes failling.  Some fail in strange ways like a PIR flood light that stays on or even start to flash.

Might be worth getting the customer to speak to the local neigbours to see if they are experiencing some thing similar?

Is there SPD type 2 and 3 at the property?  Could it be fitted?

Hire or purchase a PEL (power energy logger) from Chanvin Arnoux and leave a the property for a week or 2.  CEF and others hire them out quite cheep.

Has an EICR been done at the property recently?

How old is the current install of electrics at the house?

Be aware that some makers (Fluke for example)  make a distinction between energy monitors and power quality monitors - the latter record more events, like fast spikes, while the energy monitor is more concerned with energy use, power factor, harmonics  and brownouts. worth seeing what is and is not logged by any particualr model.
For spikes and RFI, you need an instrument with a high sampling banwidth, ideally ten MHz or more (the first hundred harmonics of 50Hz only get you to 5kHz - a sharp spike can easily be 1000 times faster. )
The good ones save it all to a memory card so you can look at the waveform, or at least inspect the statistical data created from it later.
Mike.