After looking at a lot of source material, there were a few things that seemed consistent with this phrasing.

弁リミット is a limit valve / limit switch, as you already figured out.
example: http://energy-kanrishi.com/limit-sw/

リフトアイソレ would be combination of リフト (lift) and アイソレ (isolation).
These don't appear to be used in direct combination often. The one example I was able to find was for a turbine maintenance report:

http://www.tiikinokai.jp/file/meeting/pdf/23data_08.pdf

タービン系多重伝送現場盤にて、「主タービン廻り端子台修理」の
為のリフトアイソレ時、ネジを緩める際に、端子のネジ先端が破
損してしまった。

Here it is referring to the incident of a screw breaking while being loosened at the time of "lift isolation". It doesn't give much more additional detail other than implying that section of the turbine was shut down for maintenance. It could be referring to the whole section of machinery being a mechanical "lift", or it could be referring to the location on the machine that isolates lift caused by hydrostatic pressure as seen in this valve:

https://www.shopbakerhughes.com/knockout-isolation-valve-koi...

Considering these, I would assume the phrase could be broken down as

弁リミットの (Limit Valve's)
リフトアイソレ (Lift Isolation)
に (at the time of lift being isolated/ at this section of lift isolation machinery)

Either there is a lift isolation function within the valve, and after cancelling this it became evident that the valve limit connection had not been completed.

Or - once lift (caused by some force like pressure) had been isolated from the limit valve, it became evident that the valve limit connection had not been completed.

Hopefully one of those makes sense within a larger context of the translation.