with small HP pool (i believe total under 20-30k) - each small bar represents 1k hp ... lv1 have like 2 bars, then you progressively get more and more as your total HP increases.
When you cross this threshold - each bar represents 5k HP ... and you have lets say 4 full and a half bar instead of 22 small bars.
This change is also visible when shield buff helps cross that line:
19 small green bars or almost 4 green + grey shield - totaling HP + shield above limit. you loose shiled from timeout / strip / dmg - again 19 small green bars.
Having this issue a ready to just uninstall tbh, happened twice when I activated buffs, had to reset the buffs to stop this (the health is 100% lower with the different ui as it isnt just visual)
The big bars are more health than the tick marks. You probably put a shield on then they changed appearance.
and holy crap a 5 year necro happy 2025