As observed in: https://forum.vyos.io/t/upgrade-from-1-3-6-to-1-4-0-epa1-looses-complete-dhcp-configuration/13935

l0crian@R86S# set service dhcp-server shared-network-name TEST description 'Gäste' 
  
  Description too long (limit 256 characters)
  Value validation failed
  Set failed

The above gives catastrophic failure where the whole DHCP section vanishes during upgrade from 1.3.6 to 1.4.0-epa1 according to above post.

Proper fix if its not possible to support international characters to include some kind of transformation so "ä" becomes "ae" or "a". Same with "ö" who should become "oe" or "o" and "å" who should become "aa" or "a".

Another quick and dirty method would be to replace anything that isnt a-z, A-Z, 0-9, "-" and "_" with a "." (dot) or such when migrationscripts are running.

Sidenote, the error claiming that the description is longer than 256 characters is incorrect in this case since the description is just 5 characters long.