WikiData SPARQL query gives different numbers with and without labels

Question

I am trying to download from Wikidata the journals with their OpenAlex id.

This query tells me that there are about 85k

SELECT  (COUNT (?entity) as ?entries)
WHERE
{
  ?entity wdt:P31/wdt:P279? wd:Q737498. 
  ?entity wdt:P10283 ?xopenalex_id .
}

More or less the same if I add optionally issn_l

SELECT DISTINCT  (COUNT (?entity) as ?entries)
WHERE
{
  ?entity wdt:P31/wdt:P279? wd:Q737498. 
  ?entity wdt:P10283 ?xopenalex_id
  OPTIONAL { ?entity wdt:P7363 ?xissnl}.
  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en, de,fr, ru" } .
}

But when I try to download the data I get about 20k less

both following queries return about 65k

(I wrap them in a python script using wikidataintegrator)

SELECT DISTINCT  ?entity  ?xopenalex_id  
WHERE
{
  ?entity wdt:P31/wdt:P279? wd:Q737498. 
  ?entity wdt:P10283 ?xopenalex_id 
}

and this with issn_l

SELECT DISTINCT  ?entity ?entityLabel  ?xopenalex_id  ?xissnl
WHERE
{
  ?entity wdt:P31/wdt:P279? wd:Q737498. 
  ?entity wdt:P10283 ?xopenalex_id
  OPTIONAL { ?entity wdt:P7363 ?xissnl}.
  SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en, de,fr, ru" } .
}

any idea, what I am missing ?

Thanks for any help.