Unis. fails in tutti solo/gli altri section

Can anyone help me out, please, how to interpret number 1 in bar 253 between the staves?
Until bar 252 I have a split section of solo and gli altri, in bar 253 I would like to unisono, but unis. will never show up. I also once shifted the divisi to the left side, not sure, if that had an impact on this bar.

It looks like a 1 bar multi bar rest… Something that can be fixed in Engraving options >rests I suppose :wink:

Thanks, Marc.

It turned out that I had to insert a dummy note in the upper/solo staff in order to split/divide again. It didn‘t work for me with notes in the lower staff.