Created attachment 166967 [details]
Screenshot of the observed result.

SUMMARY

Incorrect numbering sequence when using the Sequential numbering placeholder (Configure > Image Saving > Filename:)

STEPS TO REPRODUCE
1. Go to Configure > Image Saving
2. Add "Test_<#>" in the Filename: input box
3. Empty the save location.
4. Take a couple of screenshots.

I used the same steps with Test_<##> and Test_<###>

OBSERVED RESULT

Test_<#>

    Test_1.png
    Test_2.png
    Test_2-1.png
    Test_2-2.png
    Test_2-3.png
    Test_2-4.png

Test_<##>

    Test_01.png
    Test_03.png
    Test_03-1.png
    Test_03-2.png
    Test_03-3.png
    Test_03-4.png

Test_<###>

    Test_001.png
    Test_004.png
    Test_004-1.png
    Test_004-2.png
    Test_004-3.png
    Test_004-4.png


EXPECTED RESULT

Test_<#>

    Test_1.png
    Test_2.png
    Test_3.png
    Test_4.png
    Test_5.png
    Test_6.png

Test_<##>

    Test_01.png
    Test_02.png
    Test_03.png
    Test_04.png
    Test_05.png
    Test_06.png

Test_<###>

    Test_001.png
    Test_002.png
    Test_003.png
    Test_004.png
    Test_005.png
    Test_006.png

SOFTWARE/OS VERSIONS
Windows:
macOS:
Linux/KDE Plasma: EndeavourOS (Arch)
(available in About System)
KDE Plasma Version: 6.0.1
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2