By further testing, I found that this issue may be related to "Multiple reading". The variable multiplier works only if "Multiple reading" is disabled or "Continuous values" is set to 1. Otherwise, the actual multiplier used seems to be always the cube of the multiplier of the first variable with "Multiple reading" checked, while multipliers set for subsequent variables (with "Refresh" set to Never) are ignored.
This issue only affects reading. For writing, the multiplier works as expected.
This issue only affects reading. For writing, the multiplier works as expected.