That sticker would not cause any issue, the heat contact part is the raised square in the middle currently covered in thermal paste, that is the only part that makes contact with the heatsink, the rest of the CPU, the green part around the middle part is not heat producing and does not contact heatsink.
Also any issue relating to the sticker would have shown up straight away in the unit.
Please make sure that rest of cooling assembly is functional, heatsink is clear of dust, Fan is operational and heatsink is screwed down correctly to CPU.
Please also be aware that CPU has a maximum operating temperature of 100 degrees and depending on airflow, system loads and cooling design especially those that incorporate other components being cooled it can see high 80’s and low 90’s under extreme usage conditions.
Do we know what idle temperature and what load temperatures were??