Adding a font into a corporate theme

Hi guys, 

My company has a corporate theme that we need to use for all our dashboards and reporting. However it is giving me issues with the Poppins font that we need. I have installed the font on my laptop and I have amended the json file to take this font family but while it is incorporating the font into the majority of the visuals, there are 2 specific instances that is giving me a headache which I hope you experts can help. The first is the title of a visual.  Any visual that I have already created does not allow me to choose Poppins as a font for the title (see screenshot one). The strange thing is that if I create a completely new visual, the Poppins font is present in the title (see screenshot 2). Which makes me think there is a cache somewhere. Does anyone know how I can resolve this by emptying the cache without having to re-create all the visuals all over again. Second issue, the Poppins font isn't available for me to select when I use a Card visual. It doesn't matter if I create a new visual within the same PIX file. However if I create a new PBIX file and import the same theme, the Poppins font is available for me to use in a card visual. Which brings me to the same question of cache. Is there a way I could clear the cache? Thanks in advance!.

NB: Note I am going on holiday from tomorrow for 2 weeks so please be patient if I don't click 'Accept as Solution' - I'll come back to this post when I am back, thanks for your kind understanding.

Screenshot 1

Screenshot 2