This sounds awfully familiar to the issue I see. On my dual-screen setup (primary 2560x1440 to the left, secondary 1920x1080 to the right) I keep mIRC maximized on the secondary; but after every mIRC boot (which coincides with a shutdown/reboot) it opens on the primary screen (still maximized though).
I tried Window > Position > Save, but that didn't have the desired result. mIRC.ini has the following entries (not sure which ones are relevant):
I used WinAero Tweaker to change the border width on Windows 10 to be less imposing (border width is 1 and border padding is 2), which also requires the Aero Lite theme; so the position of 2558 sounds like it matches 2560 with 2px padding.
Also, for completeness sake:
Code:
//echo -a $os $version $beta $md5($mircexe,2) $file($mircexe).sig $alias(0) $script(0) $dll(0) $com(0)
; 10 7.49 97c5ea9ce0093eef4776a5ec6ab12d69 ok 9 32 1 0