Quite a few imports and exports are getting caught in the mangle at the moment. The VAT system has changed, there's a brand new border with the EU, and Covid is disrupting transport.
I don't think lights.co.uk are mis-selling, and they're not the only seller with this problem. The possibility of delivery problems from the EU is mentioned in their FAQ, and many other internet sellers warn this might be a problem. The issue has been in the news since January as well.
New customs processes and charges apply and they aren't fully worked out yet and Northern Ireland is different. Although some goods are moving freely many companies have suspended trade across the border until the details are nailed down. Other goods are being delayed somewhat while everyone involved discovers how the new system works. Importers and exporters are keen to avoid customers being shaken by unexpected customs and handling charges on the doorstep, particularly as these also attract VAT. When the system has bedded down things should return to normal, albeit slightly more expensive.
We live in interesting times!
Dave