strange result - Nested IF statement

[CodyMonster]

A	B	C	D	E	F	G	H
Reporting Date	Invoice ID	invoice payment id	invoice header id	invoice terms date	vendor number	po/non-po flag	supplier name
23-Apr-20	1900057573_5430_2020_0001064077		1900057573_5430_2020		0001064077	NON_PO	GT TRANSPORT 2012 CO LTD
23-Apr-20	1900264963_6070_2020_0001058494		1900264963_6070_2020		0001058494	NON_PO	NES GLOBAL TALENT RECRUITMENT SERVI
23-Apr-20	0027002369_6400_2020_0005508065		0027002369_6400_2020_0005508065	4/16/2020	0005508065	PO	LUSH (HEAT TREATMENT) LTD
23-Apr-20	1900004280_L410_2020_		1900004280_L410_2020	4/13/2020		NON_PO	0000315509

I'm getting the strangest result for the below nested if statement in "B". For some reason the statement doesn't pick up the supplier name if the vendor number "F" is blank.
I get D and the _ between the two cell references (D9 and H9) but not the number in column H.

=IF(AND(C9="",LEN(D9)<=20),D9&"_"&F9, IF(AND(C9="",F9=""),D9&"_"&H9,D9))

does anyone have an idea? I bet its something simple and I've been looking at this too long!

 

[DanteAmor]

This part of your formula is true

IF(AND(C9="",LEN(D9)<=20),D9&"_"&F9

C9 = "" and LEN(D9) = 20, so : D9&"_"&F9
Then 1900004280_L410_2020 " & "_" & (blank)

 

[CodyMonster]

This part of your formula is true

IF(AND(C9="",LEN(D9)<=20),D9&"_"&F9

C9 = "" and LEN(D9) = 20, so : D9&"_"&F9
Then 1900004280_L410_2020 " & "_" & (blank)

Thanks Dante,
Found something that worked.

=IF(AND(C8="",LEN(D8)<=20,F8<>""),D8&"_"&F8, IF(AND(C8="",LEN(D8)=20),D8&"_"&H8,D8))