The train operator also suffered its worst June punctuality since 2006.
Major incidents included two overhead power line problems at Glasgow Central and Airdrie, which each delayed around one in ten of ScotRail’s 2,500 daily trains. The faults contributed to ScotRail’s annual punctuality falling or remaining static for the tenth consecutive month.
It dipped to 89.1 per cent of trains arriving at their destination within five minutes of schedule in the year to 23 June - the official measure.
That was 0.2 points lower than in May and compares to 91.2 per cent last August.
However, the latest monthly performance was worse, with 88.7 per cent punctuality between 27 May and 23 June.
That compares to 92 per cent in the same period last year and 90 per cent in June 2016.
The Scotsman has been told senior ScotRail officials are concerned at the level of disruption from faults which are the responsibility of their alliance partners Network Rail.
Last month, 72 per cent of ScotRail delays were caused by Network Rail, compared to 58 per cent over the last year.
The next figures could be worse because record temperatures in the last week of June caused massive rail disruption across the Central Belt.
Rail temperatures reached 51C, triggering widespread speed restrictions to prevent buckling and derailments.
Angry passengers have tweeted their frustration. Samantha, a finance industry manager, wrote: “Not had a day yet since I started commuting with @ScotRail where they haven’t ruined my commute. Signalling issue after signalling issue.”
Matthew Verran from Dunfermline tweeted: “@ScotRail @networkrail seriously get your **** together with the signalling problems in Edinburgh, it’s DAILY.”
Kirsty tweeted: “Different day, same ‘signalling error’ with scotrail - had more issues this summer with delays than in winter. @ScotRail get your act together honestly!”
The deteriorating performance comes despite the introduction of two improvement plans, with the latest, by ex-industry chief Nick Donovan, leading to trains no longer missing station stops to reduce knock-on disruption.
Scottish Conservatives transport spokesman Jamie Greene said new transport secretary Michael Matheson “must get to grips with the chaos engulfing Scotland’s railways”, which cost taxpayers nearly £800 million a year to run.
He said: “Passengers across Scotland are growing tired of constant delays, disruptions or cancellations to their service. “Our railways are a lifeline service for many people who need to travel for work, school or to access vital public services. The very least they expect is that their train arrives at the station on time.
A spokeswoman for the Scottish Government’s Transport Scotland agency said: “We expect ScotRail to make positive steps by building on the recommendations in the independent Donovan review. “This is already being achieved with skip stopping being all but eradicated and further review actions will bring gradual performance improvement over the coming months.”
A ScotRail Alliance spokesman “June’s high temperatures caused some significant challenges and our infrastructure engineers are reviewing how we can make our railway even more reliable for our passengers.
“We know we still need to improve, and there is more to do to deliver the service our customers deserve.”