Plurals in .arb files are sometimes separated into different keys

When downloading Localazy projects into .arb files, some plurals are converted to this form:

"numberOfSessions": "{count, plural, one {{count} séance} other {{count} séances}}"

which is perfect.

Some other plurals, for a reason I ignore, are converted this this form:

"numberOfSessionsOne": "{count} séance",
"numberOfSessionsOther": "{count} séances",

which is not good.

Why does it do this? How can I solve this issue, and use only the standard plural form?