AWK -vRS=-, 48 bytes

{gsub(/[^+]/,"");x+=length;printf("%c",x--%256)}

Attempt This Online!

AWK -vRS=(.), 37 bytes

RT~/+/{x++}RT~/-/{printf"%c",x--%256}

Attempt This Online!

Uses a regex as a record seperator to split the input into seperate characters and matches them one-by-one.

AWK -vRS=-, 38 bytes

/+/{x+=length$1}RT{printf"%c",x--%256}

Attempt This Online!

Uses the RT variable in gawk to test for the - used as the record seperator.

AWK -vRS=-, 48 bytes

{gsub(/[^+]/,"");x+=length;printf("%c",x--%256)}

Attempt This Online!

AWK -vRS=-, 39 bytes

/+/{x+=length$1}" "{printf"%c",x--%256}

Attempt This Online!

AWK -vRS=-, 38 bytes

/+/{x+=length$1}RT{printf"%c",x--%256}

Attempt This Online!

Uses the RT variable in gawk to test for the - used as the record seperator.