Hi bbnovice,
I would doubt that FTTC installation work would have any direct influence on your service as all the FTTC work is in the new cabinet, except for the positioning of 2 or 4 100 pr link cables inside your existing PCP green cabinet. Note to begin with there will be no actual connections using the new link cables. Occasionally if the PCP is too cramped, then the cabinet is "re-sleeved" by lifting off the old cast iron box and replacing it with a larger new one. If that has been done it's possible that your connections have been disturbed which could cause unreliability.
There are plenty of other causes of unreliability if perhaps your exchange is being upgraded to 21CN or other cabling works are underway anywhere between your house, the PCP and the exchange.
Kind regards,
Walter