Perhaps your Function key definition table is not setup correctly.
Try running the following from PxPlus command mode (Press all Fx keys in order followed by ESCAPE)
-:list
0010 WHILE 1
0020 INPUT (0)"Hit FKey:",'BI',x$,'EI'
0030 PRINT "CTL=",CTL," EOM=$",HTA(EOM),"$"
0040 IF EOM=ESC THEN BREAK
0050 WEND
-:run
Hit FKey:
CTL= 1 EOM=$000070$
Hit FKey:
CTL= 2 EOM=$000071$
Hit FKey:
CTL= 3 EOM=$000072$
Hit FKey:
CTL= 4 EOM=$000073$
Hit FKey:
CTL=-1 EOM=$000074$
Hit FKey:
CTL= 6 EOM=$000075$
Hit FKey:
CTL= 7 EOM=$000076$
Hit FKey:
CTL= 8 EOM=$000077$
Hit FKey:
CTL= 9 EOM=$000078$
Hit FKey:
CTL= 10 EOM=$000079$
Hit FKey:
CTL= 11 EOM=$00007A$
Hit FKey:
CTL= 12 EOM=$00007B$
Hit FKey:
CTL= 4 EOM=$1B$