Living in Hertfordshire, this is where I will start. One major glaring problem is that North East Hertfordshire would end up being linked with villages in southern Cambridgeshire, even though not only is this unnecessary but also that these villages share no common interest with anywhere in Hertfordshire. The biggest problem is the connectivity between the various areas of Hertfordshire, caused mainly by the strict quota requirements, the awkward and poorly connected district of Hertsmere (Bushey has much better links to Watford and getting to Hatfield from Potters Bar is easier than getting to Borehamwood from it; Elstree & Borehamwood have stronger links with the London Borough of Barnet).
Although the BCE has stated that they may be willing to ignore regional boundaries if compelling evidence can be provided to them, I have calculated that it is not feasible to move Elstree & Borehamwood to the London Borough of Barnet for the purpose of reviewing boundary constituencies due to the strict quota limits that would make the plan unviable. ('Watford & Bushey' would have over 82,000 electors and so would 'Hendon, Elstree & Borehamwood' and the upper limit is 78,507 in this review.)
However, the constituencies in Hertfordshire need relatively little change, although as the East of England region only needs to lose one seat this is not very surprising. Here is what I personally believe Hertfordshire's constituencies should look like for 2020: