It's hard to say because they don't identify any source or reference or explain how. It does seem like speculation or conflating/confusing Type 45 issues. But they published it anyway.I think the comments on the Type 26 in the article are absurd speculation - plus, they can't even spell "superb" apparently. There's nothing, zip, zilch, nada known about the warm water performance of the Type 26, and I'm going to do with the idea that they are conflating the Type 45's issues with the Type 26 here. Neither are there any hints that the ships will have any issues maintaining speed. Yes, it'd be a lot better if we'd built a bunch of them already but most of the points in that article range from speculation to "making stuff up"
However, when looking at some specs, it seemed like the Type 26 may have a lower advertised or designed top speed than the other ships. But I would hardly think that is a significant issue or even a real issue as things like top speed area rarely actual top speeds and these days many just publish 26+kt or 30+kt and who knows what limitations there are with that anyway (noise, range, heat, electrical, etc).
I do think the Type 26 biggest problem is that they aren't building many and it isn't currently in the water. The UK (as well as other western nations) don't seem to have the same urgency. There seems to be tremendous urgency and unwavering bi-partisan commitment to defense in Australia. From Australia's perspective the UK might as well be India or Canada, off in their own world. Numbers and capability cuts all over the place, changes, time frames seem very leisurely and funding seems, disappearing and non-priority. Throw in no one seems to have a proper long term plan with brexit, or even consistency within the government, budget holes, UK is starting to look pretty flakey. Even trade talk seems to come back negative (oh the welsh sheep farmers!) or ambiguous.
Italy and Spain seem pretty focused, even though economically they seem to be under much greater pressure.
There has been some stories published about doubts regarding contingency funding for the ship building, and planed start date for steel being 2020. Pyne has shot both stories down. I think BAE wanting to push the build start date out told everyone where they are in the process. Meanwhile in Australia, I am sure some would like the build date moved further forward than 2020, like Q4 2018.