I was getting an issue where whenever I started a REPL, it would start printing outputs on the same line as the input. It would usually eventually stop. But I tried reproducing this again to see if I could figure out what kinds of things would make it stop printing on the same line, and I couldn't reproduce it. This is copied directly from a newly started calva repl with the issue, where the issue went away after an in-ns call:

; Jacking in...
; Starting Jack-in Terminal: clojure -Sdeps '{:deps {nrepl/nrepl {:mvn/version,"1.0.0"},cider/cider-nrepl {:mvn/version,"0.28.5"}}}' -M -m nrepl.cmdline --middleware "[cider.nrepl/cider-middleware]"
; Hooking up nREPL sessions...
; Connected session: clj
; TIPS:
;   - You can edit the contents here. Use it as a REPL if you like.
;   - `alt+enter` evaluates the current top level form.
;   - `ctrl+enter` evaluates the current form.
;   - `alt+up` and `alt+down` traverse up and down the REPL command history
;      when the cursor is after the last contents at the prompt
;   - Clojure lines in stack traces are peekable and clickable.
clj꞉user꞉> 
; Jack-in done.
clj꞉user꞉> 
(println "hello") hello
nil
clj꞉user꞉> 
(println "hello") hello
nil
clj꞉user꞉> 
(in-ns 'user) #namespace[user]
clj꞉user꞉> 
(println "hello")
hello
nil
clj꞉user꞉>