I did some digging in the book UXB Malta: Royal Engineers Bomb Disposal 1940-1944 and found reference on page 33-4 to an account by Major R C M Parker GM
Account of defuzing of a radio-conrolled bomb recovered from Vittoriosa or Cospicua January 1941 [1980] (National War Museum Association, Malta) . Parker likens the bomb to a PC 1400FX bomb, which is noted wasn't used until 1943. The author notes the actual physical description of the bomb Parker provides seems to indicate a 'G' mine (BM1000) or given that it is reported as sky blue a 1000 kg Easu or 1400 Fritz anti-armour bomb both of which were sky blue with aluminimum tails according to the book. It should be noted that Parker was involved in the recovery and report writing of the recovery of the first PC500 RS bomb in Malta in January 1 1942. [details attached] Given his account was written in 1980, it is possible the two incidents were conflated.
Here's a description of the January 1941 'unknown bomb incident' described by Parker a Lance Sergeant at the time:
https://maltagc70.wordpress.com/2016/01/page/2/
Sorry I wasn't able to provide anything definitive.