'perhaps the Netherlands' - it was never definite so can't be stated that they lost the jobs
From Autoexpress in 2014
Tesla UK R&D centre plans confirmed
Musk also confirmed the UK will be the base for a brand new Tesla R&D centre, which could even precede a vehicle assembly plant in Britain – if demand is high enough. “We’ll have an R&D centre here before a factory”, Musk said.
“We’ll have our first European factory in continental Europe, perhaps the Netherlands, but it makes sense to have one in the UK once we’re producing more than 500,000 units. But the factory needs to be running at full capacity [to be viable]. I’d say Model S is more European than American in design and handling. Most of the set-up work was done by British guys!”
From AutoExpress 14th November 2019
Speaking at Auto Express’s sister title Auto Bild’s Golden Steering Wheel Awards, Musk also revealed that a European research and development base was also planned for Germany, in addition to the new manufacturing plant. Later on his Twitter account, Musk confirmed that the new plant would build "batteries, powertrains & vehicles, starting with Model Y". It's understood that the Model 3, that runs on the same platform as the Model Y will follow.
Speaking exclusively to Auto Express after making the Gigafactory announcement, Musk identified Brexit uncertainty as the reason why the UK wasn’t considered for the new site: “Brexit [uncertainty] made it too risky to put a Gigafactory in the UK,” Musk said.*
Brexit might have something to do with Musk’s change of heart over the R&D centre, too. Back in 2014, he told Auto Express that he planned to build an R&D base in the UK. Those plans have since been shelved.