Some extremely vulnerable people have been told they have been removed from shielding lists via text message, without the knowledge of their GP.
This has caused confusion, with charities demanding clearer guidance for this group as lockdown eases.
GPs say they should be notified when their patients are added or removed from the lists.
Shielding has now been extended until the end of June and is under constant review, the government says.
Around 2.2 million people in the UK are staying at home to protect themselves from the virus because they were told they were at high risk of being seriously ill with Covid-19.
But 40 healthcare charities say the lack of a clear plan for their future is causing anxiety and potentially putting their health at risk.
'Doesn't make sense'
Samantha Bruce, 35, from Rotherham, has severe asthma and was told to shield on 25 March.
Out of the blue on Friday, she received a text message telling her she no longer needed to shield, and her food deliveries would be stopped.
Her first reaction was that it could be a scam, so she called her GP - but he "didn't have a clue" why she'd been sent the message.
Further investigation by her GP revealed that Samantha no longer ticked the required boxes to shield, based on her medication.
Rather than feeling reassured, she was left confused and anxious.
"It doesn't make sense - the virus isn't going anywhere so why is it that suddenly I don't need to shield anymore?"
Samantha also has two children - aged four and 10 months - to consider, and her husband is disabled and can't drive. The change in advice has thrown up questions for the whole family.
"Do I let my son go back to school?" she asks, if her risk increases by taking him there and coming into contact with other parents.
She has already decided she "won't set foot in a supermarket" anytime soon and has arranged priority deliveries instead.
But the fear of contracting the virus is still "very worrying".
"If I ended up in hospital I would have to involve my mum and dad with the children, and that's putting them at risk," she says.
Alison Cook, director of external affairs at Asthma UK and the British Lung Foundation, said they had heard of more people getting these official text messages with no explanation.
At the same time, other people have received letters asking them to shield for longer - until the end of June.
"This is an utter mess," she said.
"There doesn't seem to be any evidence or logic behind these letters and texts."
The government says all decisions about whether someone should shield are "clinically led" - in other words, made by doctors.
"Clinicians are identifying people who had initially been advised to shield from coronavirus but no longer need to do so," a spokesman said.
GPs say this is a complex process and as the guidance changes, shielding will be relevant to different people.
"However, it is important that as guidance changes, and patients are either added or removed from 'shielding lists' based on conditions they have or medication they are taking, that GPs and relevant specialists are advised about this," the Royal College of GPs says.
"This is so that doctors can communicate effectively with their patients, if they have questions."
Shielding is taking a huge toll on millions of people who have not been outside of their home since March.
They include people with cancer undergoing chemotherapy, those who have had bone marrow or stem cell transplants in the last six months and those with severe respiratory conditions, such as severe asthma.
What links them is that they are all at high risk of becoming seriously ill with coronavirus. As a result, they would have received a letter advising them to shield nearly 10 weeks ago, or been told to do so by their GP.
That means they cannot leave their house, meet friends or family or come into contact with someone with coronavirus symptoms.
'Stuck and isolated'
Sarah Davis, 29, a freelance artist and sculptor who lives in London, knows how that feels. She has not left her house for 50 days now.
She was diagnosed with Hodgkin lymphoma, a type of blood cancer, in 2017 and had to have a stem cell transplant in 2018. The impact on her immune system means she is extremely vulnerable.
Shielding started off feeling surreal, now it just "feels so unending", Sarah says.
She can't exercise properly indoors, she's had to give up all her freelance work and with the easing of lockdown measures for the general population, she feels left behind.
"We have had no new information in weeks. I feel stuck and isolated, unable to work in my art studio or move to a new house as planned," she says.
"Having been ill with cancer in the past, I do have coping mechanisms, but it is still a very triggering experience - to be locked away again and not know when it will all end."
Sarah wants the plight of people like her to be discussed at a national level so that they feel included in plans for their lives, as valid members of society.
She is not alone - a group of 40 healthcare charities has written an open letter to the UK governments, calling for consistent advice on shielding measures for extremely vulnerable people.
They include Macmillan Cancer Support, British Lung Foundation and Asthma UK, MS Society, Kidney Care UK and Cystic Fibrosis Trust - who all say more support and advice is needed as members of these people's households start to leave home to go to work or school.
Prof Martin Marshall, chairman of the Royal College of GPs, says patients should contact their GP or hospital specialist if they are in any doubt about whether to shield or not.
There is nothing Sarah would like more than to go outside and feel a sense of normality again - but she worries that when that decision is made, it could be for the wrong reasons.
"I don't want to be told to go out when it's not safe," she says.
"Staying indoors feels like a new normal - it's scary to come out of that, despite the fact I'd love to do it."