For Calc & Writer I find Spelling Dialogue freezes for many seconds at every stage (Correct/Ignore/Add to Dictionary)
Which operating system are you using?
Set to NEEDINFO.
Change back to UNCONFIRMED after you have provided the information.
I also experience this bug in LibreOffice Calc 126.96.36.199 (x64) under Windows 10. Symptoms are as described in https://bugs.documentfoundation.org/show_bug.cgi?id=93586, which may make these the same problem, with the exceptions that I get this in Calc (it's not nearly as bad in Writer), and I'm using Arial for the font.
I'm attaching the .ods I'm experiencing this on.
Created attachment 131992 [details]
I experience the bug using this Calc file on Windows 10, LO v188.8.131.52 (x64).
NEW per comment 2
This should be solved in 5.3.1 with https://cgit.freedesktop.org/libreoffice/core/commit/?h=libreoffice-5-3-1&id=53b186d85894c2c41afc025bda459db5cc6ef452
*** This bug has been marked as a duplicate of bug 105426 ***