Impossible to login or create account during checkout

-- url of the page with the problem -- : www.fifibrindecuir.fr/fr/checkout/cid-3
-- HikaShop version -- : 4.4.5
-- Joomla version -- : 3.10.4
-- PHP version -- : 7

Hi
Customers can't create new account and returning customers can't login.
I updated hikashop to the latest version4.5.1 but pb is the same.
I re-installed joomla + site to a previous version which was fully fonctional but the pb is still there ?!!
A page sometimes appears with the text

"La page n’est pas redirigée correctement

Une erreur est survenue pendant une connexion à www.fifibrindecuir.fr .

La cause de ce problème peut être la désactivation ou le refus des cookies."

The site is then blocked but after deleting the cookies from browser the site is visible again but still not working when you get to the checkout

it is possible to login with the My Account link but it is not possible during checkout

Could you help ... thank you

Hi Nicolas
Thank you for your answer.
I only have 2 languages on the site : French and English
My front end site is only in French and has been so for a year..

The problem only occurs when a new account is created or registration during checkout
I have tried with the native htaccess of Joomla and the problem remains

I don't have any problem on my wamp local server

The last order I got was on Friday and I noticed on Monday that the site wasn't working properly, I don't understand what happened during the weekend ??
I contacted my hosting company but no answer so far: my domain name is with Gandi and my site is hosted on Infomaniak, it's been like that for a few years ... I never had any pb
I really don't know what to do