what syncro is it using?
if it's the standard ford kit then they have brass bits in it to slow the gearbox down to let you engage the syncro teeth and the actual box is just too slow to slow down and it's fairly easy to "beat the box" when you are changing gears

this can also start to manifest itself by being able to slip the box out of gear when you are driving along as the bit that holds it in place gives up the ghost

if this is the case it won't lead to any major issues as it's just wear and tear and the syncro's were only £50 from ford

if that makes sense