On one of our plotter I had a similar problem.
Initially I could only print an A1 sheet @ 100% if it rotated the sheet, leaving a big blank piece of wasted paper which I had to manually cut. We were also using normal non oversized rolls.
The solution I found was to set the paper to
custom, use the sizes for an A1 sheet but
swop them in the x & y values (i.e. X was 594 & y was 841). Margins were set as normal. I then set orientation to
portrait.
The solution does not sound very elegant, but it worked on that particular plotter.
Haneef Tayob
Aziz Tayob Architects
AC23 INT rel 3003, OS X 10.14.6 iMac 3.3ghz i5 dual monitor, 24GB RAM