Could you define this in the preamble
 
%\unprotect
\defineitemgroup [Ex]
\setupitemgroup [Ex] [each] [before={\blank[medium]\testpage[1]},after={\blank[big]},option={a, columns,three,fit}]
%\protect
 
\startexercici[exercici:operacions-amb-fraccions-1]{suma i resta} Opereu:
\startEx
%\startitemize[a, columns, three]
...
\stopEx
\stopexercici
 
Good luck,

L. Montgomery

El mié., 23 de febrero de 2022 15:04, Xavier B. via ntg-context <ntg-context@ntg.nl> escribió:
On Wed, 23 Feb 2022 17:52:08 +0000
Bruce Horrocks <ntg@scorecrow.com> ha escrit:

>
>
> > On 23 Feb 2022, at 11:28, Xavier B. via ntg-context <ntg-context@ntg.nl> wrote:
> >
> > In my previous post [https://mailman.ntg.nl/pipermail/ntg-context/2022/105138.html], I don't know the reason, but the attached code des not display very well in mailing list. I put it here:
> >
> > \defineenumeration
> >  [exercici]
> >  [alternative=serried, before={\blank[medium]\testpage[1]}, text={Exercici}, stopper={.\space}, width=fit, headstyle=\ss, distance=0.25em, width=fit, headcolor=exercici_color, title=yes, titlestyle=\ss, titledistance=0em, left={\bgroup\bf}, right={\egroup}, after={\blank[big]}, prefix=yes, prefixsegments=section, way=section]
> [snip]
>
> Removing "alternative=serried" gives a more grid like layout and (possibly coincidentally) the problem of the 'c' and 'h' labels being orphaned at the bottom of the page goes away.
>
> However the Exercici 1.3 heading is now too close to the end of the previous set. Perhaps changing your "before=" setting might improve things.
>
> This is on version 2022.01.10 08:36
> —
> Bruce Horrocks
> Hampshire, UK
>

Thanks, Bruce, but removing alternative=serried is not an option.

I don't understand that 'e' fits the space and 'c' doesn't.

@Luis: joinedup does not produce changes

In conclusion, I have the same problem ;-)
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