Why are 600 Chelsea fans in Middlesbrough's stadium despite ticket sales ban?

In spite of the ban on ticket sales, a few hundred Chelsea fans did manage to make it up to Middlesbrough for Saturday's FA Cup clash.
The Blues are playing for a spot in the competition's semi-finals against their Championship opponent at the Riverside Stadium.
But the tie has been overshadowed by issues caused by the restrictions placed on the club and owner Roman Abramovich in the wake of Russia's invasion of Ukraine.
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Why are Chelsea fans allowed to attend Middlesbrough match?
During the week, Chelsea released a statement in which it was confirmed that no tickets would be made available for sale at the Riverside.
The Blues even requested the game be played behind closed doors; a suggestion that met with a withering response from their opponents.
Chelsea's 600 strong away end pic.twitter.com/hm5SjOjMxm
— Nizaar Kinsella (@NizaarKinsella) March 19, 2022
So why, then, was a small contingent of Chelsea fans present for Saturday's game? Simply enough, because they managed to purchase the tickets before the Londoners were obliged to send them back.
When will Chelsea be allowed to sell tickets again?
Chelsea's ticket restrictions do not apply to season ticket holders, who are still able to attend matches as before.
But for the rest of the fanbase, and for away games, no end is in sight, though the Blues insist they are doing all they can to lift the ban. "We are pressing the Government to allow our supporters to have access to tickets," a club statement explained on Monday.
"Meetings are taking place daily in search of a resolution. In addition, the Premier League and FA are also discussing with the Government the sporting integrity issues raised if they do not permit fans to attend.
"We are aware of the high level of frustration our supporters are facing over this issue, and we are doing everything we can to resolve it as soon as possible."
When will the new owners be announced?
Away from the stands, Chelsea are also engaged in a takeover process, as Abramovich seeks to cut his ties with the side following the freezing of his United Kingdom-based assets.
The deadline for new bids passed on Friday, with some 30 potential buyers submitting their proposals, and a shortlist of three or four final candidates is expected to be ready by Monday - with the club hoping that a takeover can be completed by the end of the current month.