On 26 January 2020, Wallace was suspended from the soap for two months due to her off-screen behaviour; she ultimately returned to work when production of the series resumed during the COVID-19 pandemic.

Kat's storylines also include suffering a miscarriage, an affair with Derek Branning (Jamie Foreman) which briefly ends her marriage with Alfie, becoming penniless and permanently scarred in a fire and becoming a millionaire.

Since her reintroduction to the show in 2018, Kat's storylines have focused on the breakdown of her and Alfie's marriage and her separation from Tommy and their twin sons Bert and Ernie; a relationship with Kush Kazemi (Davood Ghadami); feuds with both her cousin Stacey Slater (Lacey Turner) and enemy Phil Mitchell (Steve McFadden); embarking on a relationship with Phil after sleeping with him; surviving an accidental hit-and-run by her friend Whitney Dean (Shona McGarty); taking temporary custody of Tommy's half-sister Scarlett Butcher (Tabitha Byron); a feud with Scarlett's mother Janine Butcher (Charlie Brooks); clashing with Phil's sister Sam Mitchell (Kim Medcalf) and his ex-wife Sharon Watts (Letitia Dean) over the Mitchell empire; her tumultuous marriage to Phil, ending in their separation; suffering parental abuse from her son Tommy; and reconciling with Alfie.

Fiercely defensive of her sisters, Kat embarks on a feud with Little Mo's abusive husband Trevor Morgan (Alex Ferns) – though has a fling with Lynne's boyfriend Garry Hobbs (Ricky Groves).

While she and Alfie are absent, James, the newborn son of local resident Ronnie Branning (Samantha Womack), dies of sudden infant death syndrome.

When the nursery raise their rates, Kat is forced to leave the children in Mo's care to work her shift at the market, but ends up having drinks with Kim Fox-Hubbard (Tameka Empson).

When Kim returns with Shirley Carter (Linda Henry), she confesses her fears about being a bad mother, resulting in the other three women sharing their experiences of motherhood and reassuring her.

The next day, following a conversation with Shabnam Masood (Rakhee Thakrar), Kat changes her mind and throws the letter away but Mo retrieves it and posts it on her behalf.

Later, a content Kat returns to Walford and tells Stacey and Alfie that she has finally made her peace with the past and is no longer willing to let Harry control her.

It is revealed that Iris Dolan (Orla Hannon) lost a baby in London and brought Dermott back as her own, and her husband Peter (Stanley Townsend) does not know the truth.

Kat returns to Walford and is confused that The Queen Vic is holding a benefit night for her and confronts Mo, but hides when Ian brings the raised money.

Bianca's stepdaughter Whitney Dean (Shona McGarty) asks Kat to cover her stall as she is being stalked by Leo King (Tom Wells).

Whilst having celebratory drinks in The Queen Vic for Whitney's release from prison, Kat is contacted by an unknown person for help and briefly leaves Walford.

During the COVID-19 pandemic lockdown, Kat and Kush face financial problems which are funded by Stacey, from money that she stole from Ruby Allen (Louisa Lytton).

When Suki Panesar (Balvinder Sopal) increases their rent payments, Kat organises a heist alongside Kush, Phil, Ben and Shirley.

When Kim reports Phil's involvement in Vincent Hubbard's (Richard Blackwood) murder to the police, he attempts to leave Walford with his son Raymond Dawkins (Michael Jose Pomares Calixte).

When Tommy accidentally stabs his bully Sid Bello (Buddy Skelton), Phil summons his sister Sam Mitchell (Kim Medcalf) back to Walford to look after his businesses whilst he is in prison, leaving Kat unimpressed as she still holds resentment towards Sam for letting Zoe believe that she had killed Sharon's adoptive father Den Watts (Leslie Grantham) all those years ago.

Kat is later devastated when she hears from Sam and Sharon that Phil has been killed in prison, but he returns on the opening of Peggy's wine bar, after taking a deal to become an informant for DI Samantha Keeble (Alison Newman).

Kat’s nephew Freddie (Bobby Brazier) decides to search for his estranged father, Graham Foster (Alex McSweeney), despite the Slaters' objections.

"[8] It continues: "With her enemies closing in, there was nothing to do but return home to Walford for help, complete with a huge baby bump"[8] Unwanted pregnancies, suicide attempts, miscarriages – Kat has been through it all.

[10] Wallace was intended to depart in December, however a pregnancy scare meant that she was forced to stop filming in August, and scripts featuring Kat subsequently had to be re-written.

[14] A spokesperson for the show praised Wallace's talent and thanked her for her contribution to the series, stating that "Jessie and the writers want Kat Moon to go out on a high.

"[29] "The storyline presented Ronnie with grief, disbelief and anger and the temporary breakdown of her relationship as well as her gradual coming to terms with her loss and the efforts to re-build her life following the tragedy.

It is Ofcom's view that the broadcaster did not intend the storyline to suggest that her actions were a typical response of a mother who had experienced SIDS and therefore sufficient editorial context was provided to viewers."

[41] Marsh wrote in her magazine section: "Last week, EastEnders was cleared of wrongdoing by Ofcom, the media regulator, over its baby swap storyline, and I think that's the right decision.

Speaking about the show, Wallace commented: "I have always loved working on EastEnders so when I heard of this new drama to take Kat and Alfie outside of Walford, I couldn't believe our luck.

[61] Treadwell-Collins confirmed that "the discovery that Kat has a secret son will [...] ultimately lead to the Moons realising that the answers to so many questions lie across the sea in Ireland.

"[62] Director Jesper W. Nielsen said the series is "About how one woman's search for a lost child opens Pandora's box; revealing the terrible lies and secrets in the little village of Redwater".

Yorke commented: "The Slaters are one of the all-time great families in EastEnders and Albert Square has never felt quite the same since they scattered to different ends of the country, and in some cases beyond.

[92] Laura-Jayne Tyler of Inside Soap enjoyed Kat's 2018 reintroduction and said that Wallace returned "on full gas, giving nothing less than her trademark powerhouse performances".